- "How to prove it" by Daniel Velleman is one of the classic textbooks to introduce proofs that many students praise.
- Lecture notes for MAT102H5, by Shai Fuchs. This is an introduction to proofs course taken by math and CS students at UTM.
- Playlist 1 for MAT137: a collection of videos on logic, notation, definitions, and proofs.

Notice that reading proofs or watching somebody else write proofs will not help you by itself. The only way to learn to write proofs is to get your hands dirty. You need to practice writing your own proofs (which will likely be bad at first) and get feedback on them.

If you have other suggestions that could be added to this list, feel free to let me know at "alfonso (at-sign) math (dot) toronto (dot) edu". Thanks!