LSE is the last step of Roux method, its the 4th step in which you solve the last six remaining edges, hence LSE

4 edges are on the top, and 2 on bottom, hence 6 edges. LSE can be broken down into 3 mini steps

First step, is 4a and you solve Edge Orientation

Here you make all the sticker on top and bottom, either white or yellow

In this case, I have green and red so I switch them up and make all stickers white/yellow

Next step is solving UL/UR edges which is solving the right side of the cube, and the left side

In this step, you solve the edge that comes in here and the edge that comes in here

For solving this step, you keep both the edge in bottom

and then you just put them on the top like this

and then you solve this side and this side

The last step is called 4c in which only the middle slice is left to be solved

and you solve the middle slice by doing one alg like this

Those are the 3 steps of LSE

4a is solving edge orientation EO. 4b is solving UL/UR edges and 4c is solving the rest

Now we are going to get indepth into these steps

First step of LSE is called edge orientation and in this step you get all the edges to be either white or yellow

and in this step, we are introduced to the concept of bad edges and good edges. Good edges are edges which already have white/yellow on top like this one

and bad edges are those edges that do not have white/yellow on top. Red is bad edge, green is bad edge, blue is bad and this is good edge

And the most important case of EO is called Arrow case. In arrow case you have 3 bad edges on top

and one bad edge will be in the bottom

Now if you have yellow or white facing towards you in the bottom piece, that means its a bad edge

otherwise if you have any other sticker like green/red that means, its a good edge

This is the arrow case, 3 on top and one on bottom and for solving this when the edge is in the front

you do M' and then you do U or U' and you do M' once more

and this is the next arrow case and this is from the back and one important thing to remember when recognizing bad edges and good edges

is that bad edges will always come in pairs, so there will never be odd number like 1/3/5 and they will always be even 2/4/6

For example, I see 3 bad edges on top and this is not a bad edge. Because bad edges always come in pairs

the last bad edge is at the back as 3+1 is even no and bad edges always come in pairs

and for solving the arrow case with edge at the back, you do M U or U' and then M'

Now we are going to go over each of the EO cases and first I'll show you the beginner cases and then more intermediate ones

First we are going to start with 2 flips and this is the first case and in this case you have 1 in here

and one in here, and this can be either vertical like this or horizontal like this

and for solving this 2 flip case, you do M' U' M

for getting the arrow and you can solve the arrow by doing M' U' M' or M move

Now the same 2 flip case can be in the bottom and for solving the case when its in the bottom, you do this

M' U' M' which gives us the arrow case and then you can solve the arrow

This is the next 2 flip case and you have both of the edges adjacent to each other

and when you have these two in this position, at the back and the right, you do this

M' U' M' which brings us the arrow case and then you just solve the arrow case

this is the same 2 flip case as before but now you have the edges in right and front

and you can always do U' and solve from here, but if you want to be even more efficient, you can solve it from here too

but doing M U M which brings us arrow case and then you solve the arrow case

this is the same 2 flip case from U2 angle and for solving this you do M U' M'

which gives you arrow from back and then you solve arrow case

and this is the same case from U' angle and for solving this you do M' U M

which gives you arrow case from front, and you solve arrow

do remember one thing, arrow cases from front start with M' move and then you can do U' or U move

and then you can either do M or M'. Only the first M' move matters, after that you can do U, U', M, M' and the EO will still be solved

same goes for the arrow cases from the back. Only the starting M move matters

then you can do U, U', M', M and the EO will still be solved

this is the last 2 flip case and you have 2 edges like this

one on the top and one on the bottom, and when you have the case like diagonally opposite from each other, you do this

M U' M which gives you arrow and then you solve the arrow case

and you can get the case like this and this is just the mirror case. Instead of using M moves, you use M' moves

For solving this case, you do M' U' M' which gives arrow case and then you solve arrow

Now sometimes you may get cases like this where you have edge on the side, instead of being on the top

and in these type of cases, instead of doing U and solving it, you can solve it from here too saving 1 move

the thing that you have to do is insert the edge, where the good edge is

In this case, I have the bad edge at the back, so I insert the edge in here with M' U M

and that will give me the arrow case from the back so I can just solve arrow cased

and when you get the case like this with the bad edge in front, you insert the edge at the back with M U M'

and that will give you the arrow case from front and you can solve the arrow case

Now comes the 4 flip case and in this case, you have 2 bad edges on the top, and 2 on the bottom

and for solving this case, you keep the bad edges on the top in horizontal line and these will be vertical

and for solving this you do M' U2 M'

That will give you the arrow case and you can solve the arrow case

This is the next 4 flip case and in this case you have all the 4 edges on top like this

and for solving this case you do M' U2 M' and then you solve the arrow case

This is the last 4 flip case and here you have 2 bad edges on the top and they are adjacent

and 2 will be at the bottom and for solving this, you keep the bad edges anywhere you want

Keep the bad edges anywhere and do M2 and then solve arrow case

for example, I can keep this in here and do M2 and I get the arrow case

and then I can just solve arrow case for solving this EO case