Help with a common trap.

Post the actual game ... will help to get some insight as to how you ended up in this situation.  Did you miss looking at his forcing moves? Did you play a natural looking move that led to a tricky shot (as most traps tend to originate) or did you completely mis-evaluate the dangers in this position? We won't know until we look at a few games.

Update:

I looked at your earlier online game that led to resigns in this exact position. Your opponent pins the knight on f3 with the bishop and then hits it again with Nd4. You had the option to break the pin with Be2 or even something like h3 but you chose to ignore it and played d3 ... leading to the obvious Bxf3/gxf3/Nxf3 busting up your castled king, leading to other complications and mostly "resigns" like situations.

A common theme in some games is to pin the knight after your opponent has castled and try to put additional force on the pinned piece.

This is not really a trap (the same way Qh5 + Bc4 is NOT a trap)  but more of you not paying attention to your opponent's forcing threats ... the remedy is quite simple ... in the future, watch for pinned pieces and how they can be exploited.   You'll be sure to find a candidate move that addresses this threat. :)

You missed a trap- that you should be aware of given your opening. 6. Nxe5 Although it gets tricky after de QxB Nxc2

The thing is not to trap your white bishop out by d3. If you don't block it out you can defend like so...

Hey worther... When the opponent's bishop pins your knight (for your queen), put your bishop in the middle of bishop and queen. Then he wont have his bishop. If you somehow keep the knight, and that position happens, move it to H4. It protects the square of checkmate and attacks the queen. DO NOT move the G-pawn up. Hope this helps!

after 6 Nxd5 and Bxd1, white chechmates with 7 Bxf7+!! then Nd5#

Legall's mate eh?

Just some ideas. Not the best player so I may have missed out on some stuff. Our styles also may be different.

5. I'd have moved 5. h3 to kick his bishop back and then 6. Nxe5.  If his bishop takes your queen, you've got mate in to with 7. Bxf7 K-e7 8. N-d5++

If he wisely captures your knight with 6...Nxe5, you take his bishop on h5 with your queen threatening mate and your up a pawn.