What should be my approach

#1

How should i move forward in solving this problem, like how should i think to solve a DP problem

#2

Think of it as if you place 1xm tile horizontally then you will have (n-1) rows left. Another option will be if you placed the tile vertically then you are left with (n-m) rows to put the put the tiles.
So recurrence will be -:
f(n) = f(n-1) + f(n-m);
Think of base case yourself.

#3

can you please explain that (n-m) rows will be left if we place a 1*m size tile vertically

#4

You have n rows and if you place 1*m tile vertically then you occupy 1 column and m rows, so you left with (n-m) rows. Sketch it in a notebook , you will get it.