Help needed understanding tab notation...

Hi folks,

Well after a 17 year break, I've decided to take up the (electric) guitar again and subsequently found this site which is really great!

I'm able to remember how to play the chords but one thing I'm having difficulty with is understanding the tab notations on this site..

for example i've copy and pasted a section of "Good Times, Bad Times" by Led Zep below.

E|-----------------|-----------------|-----------------|-----------------|
B|9-9-------------|9-9-------------|9-9-------------|9-9-------------|
G|9-9-------------|9-9-------------|9-9-------------|9-9-------------|
D|9-9-------------|9-9-------------|9-9-------------|9-9-------------|
A|7-7-------------|7-7-------------|7-7-------------|7-7-------------|
E|-----------------|-----------------|-----------------|-----------------|

In the example above, do I strum the:-

E|--
B|9-
G|9-
D|9-
A|7-
E|--

or play the strings individually?

Further on in the song the notations change from being in-line with eachother to being staggered...

                 Verse 1
E|-----------------||-----------------|-----------------|
B|9-9-------------||9-9-------------|--7-7-----------|
G|9-9-------------||9-9-------------|--7-7-----------|
D|9-9-------------||9-9-------------|-7-7-7-4-7-------|
A|7-7-------------||7-7-------------|5-----5--4--5-6-|
E|-----------------||-----------------|-----------------|

...and i presume I play the staggered notations individually..

So basically when the notations are in a line vertically does that mean you strum and when they're staggered you pick individual strings???

Any help would be really appreciated!

Thanks folks