Gathering a shrub when its tile is " or ♣ will result in something like grape vines or potato plants, which may or may not be usable. Think of it as your dwarves ripping the growing plant out of the ground. If you want actual grapes, you will have to wait until the tile changes into a % and then designate it for gathering.
If you're using a graphics pack, you can (k) over the shrub to see if it lists something like "grape vines, grape leaves", "grape vines, grape leaves, grape flowers", or "grape vines, grape leaves, grapes". The first and second results will yield grape vines only, the third will yield grapes. The names you see may vary based on the raws for that shrub, but the first name will always represent the plant, the second the leaves, and the third either the flowers or fruit.
Continuing with the grape example, brewing from plants at a still should use grape vines to produce wine. Brewing from fruit will use grapes to produce wine. You need to select the appropriate option based on whether you've gathered plants or fruit before your dwarves will make booze. I recommend keeping all your produce in a stockpile and deleting any burrows you might have.
I am 90% sure I was able to use both grape vines and grapes to make wine, but if you still can't use the vines for anything, wait until you get a bunch of purple %'s and then designate the ripe grapes for picking. Those should be usable under the "brew drink from fruit" option.