When Bad Goes To Worse ...

f6, hmm, bad defence, it's really from a bad position, and making it worse to checkmate.

You need to focus on chess principles and simple tactics. In the first game 6.- Nd5 is a really bad move. It doesn't loose material but it's a waste of time. You just help White to build a strong center with c4. Then after Nb4; a3 the knight lands completely offside on a6. There is a simple rule in chess: Don't move a piece two or more times in the opening. Of course there are many, many exceptions from this rule but for starters I would just go with it.