17: The q6-r5-q4 shape (with various stones on q7-r7-r6) occurs a lot in Go. P4 is a very good follow-up move for W. (Play around with the variations and see if you can figure out why.) As a result, B often finishes up the sequence by playing o4, p5, or some other move that denies W that follow-up before moving elsewhere.

24: O17 is a bit of a scaredy-cat move. The general rule in go is, the lower you press down your opponent, the worse off he is. On the first line he gets no territory, on the second line he gets 1 territory per stone, etc. (You also need territory to live, so the less territory a group has, the weaker it is.) Sometimes in situations like this, the smart thing to do is march on along the third line (o18), sometimes to push him down even further with a diagonal bend, blocking of his stones (o19, a "hane"), but you never want to give up ground.

61: Notice that after playing 59 to test your response, W doesn't bother to save the stone by connecting it yet - white thinks there are still bigger moves on the board, so he wants to keep the initiative ("sente") rather than making a second-line move to which you don't need to respond ("taking gote"), with would give you the initiatve. Compare this to earlier moves at A9 and T6, where you decided that defending on the first line was the biggest move.

Fun game, lots of good moves for a beginner - I didn't mention every single mistake, partly because I'll bet you've already figured some of them out yourself, partly because you'll understand the mistakes better with more play.