The main thing you need to know about saving is that you've got three different ways to do it through the pause menu manually with f5 for quick saves and the game's own autosaves. Your manual saves are really the most reliable giving you 31 slots to work with which is pretty generous. The trick is keeping at least three different manual saves going, so you can always roll back if something goes wrong especially before big story decisions or when you're about to enter somewhere dangerous.

Quick saves and autosaves share 19 slots between them but honestly, don't rely on those too much. The game will autosave when you change areas or hit certain story beats, but it won't catch everything like when you find good loot or make important trades. One thing that's really helpful is backing up your saves folder which you can find in AppData/Local/Stalker2/Saved - just copy that somewhere safe every now and then.

Tip: saving during fights won't work and trying to save during emissions can actually mess up your save file so wait till you're somewhere safe. Maybe interesting - if you're moving saves between devices turn off cloud sync first to avoid any weird conflicts. Just remember, manual saves are your best friend, and it's always better to have too many saves than not enough when you need to load back.