Before an adjective, troppo means "too" and abbastanza means "enough" or "quite", and neither changes: troppo grande, abbastanza lunga. Before a noun, troppo agrees (troppa gente, troppi vestiti) but abbastanza still does not.
Examples
- Questo maglione è troppo piccolo.
- This jumper is too small.
- La giacca non è abbastanza calda.
- The jacket isn't warm enough.
- C'è troppa gente qui.
- There are too many people here.
The mistake to avoid
Before an adjective troppo never agrees: troppo grande, never "troppa grande".
Where this fits in
Colours, clothes & likes, Italian A1: Name colours and clothes, buy something in the right size, and say what you like and don't like.