The strings of an acoustic are much higher in gauge than a normal electrics because the thicker the string (normally) the louder it is, and the more full the tone. With an electric it doesn't need to be loud or necessarily full because you can rely on the pickups or amp to get the loudness and tone for you.

I would suggest getting a set of 11s if it's your first acoustic.

EDIT: Technically you can use your electric strings on an acoustic, but I wouldn't suggest it. It won't hurt your guitar, but it won't sound good either, infact it will probably sound really bad. They will also break pretty easily I would imagine.
Quote by mzhang13
Are they made any differently?

yes different material.
But all acoustic string are different.
I prefer a bright sound for acoustic.
I buy ghs bright bronze 12s.

12 are standard gauge for acoustic.

elixers coated are made with a coating to help keep the brightness,
but some say they are dull when you put them on b/c of the coating.

any other questions, feel free to ask.
Acoustic strings are heavier gauge because of the extra energy required to move the soundboard of an acoustic guitar. The vibrating string energy needs to be transferred to the soundboard and start that resonating. Typical electric guitar strings just can't cut the mustard here, so a thicker string is required. You can use electric strings, but the guitar will sound dull and lifeless. As already stated, .012's are the norm for acoustics.