Is it common for a white-ish see-through liquid substance to come out of a vagina?

yes- vagina discharge - it is how your vagina Cleans itself- All females have it

Discharge and secretions from and of the vagina are a normal, healthy part of how that anatomy works and part of the reproductive system functioning, even if they somehow seem weird.

The vagina -- which is not the whole of that genitalia, called the vulva, but the flexible tube behind the vaginal opening and inside the body -- is a passageway between the outside of the body and the internal reproductive system. The pH balance of the vagina is acidic, with "good" bacteria that has co-evolved that helps keep infections away. Vaginal secretions are how the vagina cleanses and regulates itself -- how amazing is that? -- in the same sort of way that saliva helps keep our mouths clean and healthy.

Normal discharge

is clear and thin -- that sort of discharge usually occurs around ovulation, and vaginal secretions during sexual arousal may also have this appearance

is white or slightly yellowish and thick (but does NOT have curdy "chunks") -- much like the consistency of paste, this sort of discharge tends to occur during less fertile times in the monthly cycle

has a mild but not unpleasant odor or scent

may have a brown tint just before or just after menses.

is generally moderate -- not too profuse or too scanty

will appear on your underpants, or on your inner labia a lot of the time

Normal discharge is just that: normal. It's not anything to be scared or embarrassed about, there's nothing wrong with it, and vaginas need it around to stay healthy. We don't worry about the saliva that's in our mouths, or worry it might be gross, and the same goes here. Without these discharges, we'd have some problems -- infections more often, uncomfortable sex and the vagina would start to smell pretty darn funky, just like our mouths do when they don't stay clean and hydrated. We need all this slippery stuff.

Discharge that is NOT normal, but a likely signal of infection or illness may:

be chunky or very heavy, with small curds like cottage cheese

be very watery, or consistently profuse

have a strong odor

be grayish, greenish, yellow or pinkish

http://www.scarleteen.com/article/bodies/honorably...

It's just discharge.

Discharge will change with hormonal changes, you can get clear stretchy discharge like egg-whites when you're fertile (from around a week before ovulation, which would typically be 2-3 weeks before menstruation).

If it's more sticky like snail trails it's lubrication, this occurs from the first stage of arousal as it is needed to help prevent friction during penetration - in your pre-teens and teens hormonal surges can cause lubrication to occur even if you don't feel especially aroused, just like how teenage boys can get random erections.

yes that is perfectly fine