Step-3
Solving 2nd/middle layer

Now, look for an edge that does not have yellow on it.

Look at the 2 colours on the edge. Match the front colour with its respective center, like this:

• 

• 

If you get the first case shown above, do this algorithm:
R’ U’ R’ U’ R’ U R U R U
It can be remembered easily by seeing how it moves here:

If you get the second case, do this algorithm:
F U F U F U’ F’ U’ F’ U’
It can be remembered easily by seeing how it moves here:

If you get a case that is like this:

Then just do any of the above algorithms to bring the edge to the top and repeat with the new case.