you should wear an under shirt if you can see your bra.
Depends on the bra and the dress. You need a dress with a good strong back (not elastic or too low), and if the dress is strapless its best to use a strapless bra.Put the bra on under the dress and put pins through the dress side seams into the bra (make sure not to poke yourself!).Pull out the front of the dress and make a mark on the bra straps where they meet the bottom of the dress straps or the top of the dress. Undo the back of the bra and take the dress off carefully (you may need help).Mark the bra and the dress where the pins were before you unpin it.Cut the back off the bra just beyond your marks then sew the sides of the bra onto the dress sideseams along the marks.Pin the bra straps onto the dress straps as you marked before.Put the whole thing back on and make sure that it all sits properly. You might need the straps a little looser than before.When you are happy take the dress off and sew the bra straps onto the bottom of the dress straps/top of the dress wherever you pinned it before and cut off the rest of the bra straps.Make sure to finish the cut edges of the bra if you think they might fray or show.
a strapless bra
Your underwear & maybe a bra (depending on how the dress is built). For example, some dresses have a bra or push-up bra built inside; others are very strappy or have none at all, so not wearing a bra or wearing a strapless one would look better.
It's not because it feels good. It's because no one wants their bra to be visible under the dress (which it would be if the dress was low-cut like you mentioned.)
you can see them by looking a girl look at the breast (without her noticing if she does then your in trouble) or you can them if they have a see thourgh dress with no bra
Some girls do wear a bra with a dress it all depends on what kind of dress it is. like if it is a strap less dress then don't but if there are some straps then usually you do.
Yes, it is weird and it would look tacky to do so. Go to a department store and buy a bra to wear with a strapless dress. Look in any fashion magazine and you will see that it just isn't done to have a bra with straps showing in strapless dress.
Under your bra is boobs or breasts
A bra is for support and a slip is to make sure a dress is not see through. If the girl already wears a bra, and she needs a slip, she can easily wear them both. Depending on how much support and the dress she needs, she could choose to wear only one or the other.
Its like a push-up bra!
To cover the bra so its not see threw or to hide fat
There is no need to wear a bra under a sports bra, because sports bra has the function of supporting breast at right position, the key point is that you need to choose a good sports bra.