Do the tutorial - listen to the dialogue & read the notes...

You just keep getting dumber and dumber.

Who ties your shoelaces for you in the morning?

Maybe I'm dyslexic savant.  If I filter out everything others have to say,
I'll have everything I need to know.

As stated by someone else, the best explanation of the HEV suit is in the
tutorial (the Hazard Course).  Do that, and you'll know as much as we know.

There are three types of save in HL: autosaves, quicksaves, and full saves.

Autosaves are made by the game automatically every time you pass an autosave
point, usually where a new area of the map loads (which you might not notice any
more with modern CPU speeds, but there used to be a short pause and a
"Loading..." message). There are two autosave slots, which are continually
overwritten as you pass further autosave points.

Quicksaves are made by you, every time your press F6. Like autosaves, there are
only two quicksave slots. Every time you press F6, you are not creating an extra
save slot, you are overwriting the older of the two quicksave slots. Thus
quicksaves are not permanent and should only be considered as a sort of
"bookmark" of your current progress through the game. Some people do not seem to
be aware of this. You cannot revisit earlier parts of the game if you only use
quicksave.

Full saves are made by exiting to the menu and saving from there. If you want to
make a permanent save that won't be overwritten, enabling you to return to it at
any time, this is the one you want. I recommend you do this at least once every
chapter(1). Some people have got themselves stuck in positions they can't get
out of, quicksaved twice in their panic, and then found there is no way to go
back other than to start the game from scratch. Very annoying if you are a long
way into the game. It's rare but it happens, so MAKE FULL SAVES!

As for which save loads when you quickload with F7, I think it is your most
recent save, whether that's autosave, quicksave or full save (I might be wrong
about the full save). Thinking about it logically, it'll be this way because it
only has to load your situation within the current map, not go back to a
previous map with consequent lengthier loading time. The furthest you will ever
go back with F7 is therefore the last autosave, as any quicksave or full save
further back will be a different map. If you load from the menu, you can choose
any save you like.

The save system was slightly modified in HL2. It still has autosaves, quicksaves
and full saves, but you can also return to the start of any previous chapter.

(1) Chapters are the named areas of the game, such as "Anomalous Materials" or
"Unforeseen Consequences", aka levels, though Half-Life was the first game to
introduce a continuous playing style with no overt levels or lengthy loading
screens, just a relatively seamless pause as you traversed an empty corridor.

--
Paul