Celeste

Strawberries are the main form of collectible in Celeste, with a number hidden throughout each chapter (aside from chapter 5), and 175 in total. Helpfully, the chapter/sub-chapter selection screens include a checklist showing which you've already collected (note that there are no strawberries in the B-side or C-side variants of each chapter). The difficulty of collecting the strawberries varies quite a dramatically - some are in the open and fairly easy to collect, many require challenging platforming scenarios to be completed, and there are also a good number that are fairly well-hidden and/or away from the main path through each chapter.

To collect a strawberry, you'll first need physically to reach it, but this in itself isn't enough, as the strawberry will then follow Madeline, floating behind her, but dying will cause it to return to its original location; to collect it permanently, you'll then also need to return to safe ground without dying. Also, as well as standard strawberries, found floating in place, there are a few flying strawberries, a variant appearing with wings - these present a further complication, as using Madeline's air dash ability will cause the strawberry to flee, and you'll then need to be quick to collect it before it leaves the area (dying will, as usual, reset the strawberry's position).

The video walkthroughs above for each chapter include the location of all strawberries. Alternatively, if you prefer text and fixed screenshots, I'd recommend IGN's collectibles guide, as linked below, which includes a breakdown by sub-chapter (note that in a few cases, the numbering of the strawberries doesn't quite match up with the in-game checklist, but it's mostly correct). The IGN guide also includes an alternative video walkthrough for each strawberry (and other collectibles), cutting out the parts of each chapter that don't relate directly to these collectibles.

https://uk.ign.com/wikis/celeste/Walkthrough

Finally, note also that after completing all B-sides, upon replaying each of the standard chapters and B-sides you'll find a golden strawberry near to the start - these are the ultimate challenge in Celeste, as after activating these, they'll follow you through the stage and won't actually be collected until the very end - and you'll need to do this without dying even once. The C-sides also each have a golden strawberry, which will appear upon re-entering the chapter after beating it once. Fortunately, no trophies are tied to the golden strawberries, but they can be used to contribute towards the 175 required for this trophy, if you find that you're having trouble with any of the normal strawberries.

As a walkthrough for chapter 8 (there are no trophies tied directly to its completion) isn't already included above, here's a walkthrough for this final chapter, once again with credit to YouTube user The Triple S League:

https://www.youtube.com/watch?v=4zGdg2C2yyM