EFLC is on sale too for $9.99 http://store.steampowered.com/app/12220/
GTAIV Complete Edition (includes Grand Theft Auto IV and Episodes from Liberty City.) is on sale for $14.99 http://store.steampowered.com/app/901583/
Grand Theft Auto Complete pack is on sale for $24.99 (GTAIII, GTAIV, EFLC, GTA:SA, & GTA:VC) http://store.steampowered.com/sub/4466
These sales end on the 23rd, again just a friendly reminder, to wait until the end of the sale before buying any game as that game may go on sale during one of the 24 hour or 8 hour sales.
Now, to answer your questions:
The next 8 hour sale starts at 4PM PDT/GMT -0700. Every eight hours on the steam home page they are letting the consumers/members vote on the next game to go on sale for that deal. The Steam Summer sale games start at every morning at 10AM PDT and last up until the last day. Generally on the last day, steam will put the best/highest selling daily deals of the entire sale period backup for the remainder of the sale. Also, keep your eyes open to the lower right side, as they have been having flash sales, these will most likely be not that popular titles and the times of these sales vary.
Steam is a game distribution network created by Valve (makers of Counter-Strike, Half-Life, Portal, Left 4 Dead, & Team Fortress series).
With you steam you sign up for an account, download the steam application and purchase games. Steam offers voice chat, in-game overlay, friends lists and other features. The cool thing about having all your games in steam is if you get a new computer, almost all of the games on steam are DRM manged through steam which means that you can reinstall/re-download very easily (compared to having to reactive a cd-key). You can read more from on the their wiki page:
http://en.wikipedia.org/wiki/Steam_%28software%29
Disclaimer: I am just an fan of most of Steam's policies and sales (most of them).