If I use my external HDD for Time Machine, can I use it to store other files too?

Yes.

 

You can use the drive for other files as well. You can either just throw them on there or make a separate partition for your backups.

 

Before you start the time machine process go applications/utilities or (cmd+shft+U in finder) and select disk utility. Select your the root external drive and then there should be a tab called partition (if there isn't you havent selected the root of the drive) select your partition arrangement-in this case 2 partitions, i'd opt for a larger time machine partition that second partition but it does depend on your HDD space.

Then name your 2 partitions, hit apply/go/energise and it should only take 20 seconds. Make sure you partition the drives as Mac OS Journalled (else time machine wont like it)

The main advantage of 2 seperate partitions is if something should happen to one partition but not the other (i.e incorrect permissions and file settings) its not necessarily the be all and end all of all things good. (Or thats the way i think of it- hence i have about 6 different partitions on the same drive!) ;-)

PTP

 

Partitions will make things more organized. Basically its like a big room that you put up walls in and dedicated each room to difference things. One "room" can be used for time machine while the other "room" can be used for files and other things.