Drive storage is pooled per seat: your workspace's total capacity is the per-seat allowance multiplied by the number of seats on your plan, so your space grows as your team grows. A workspace-level override can be set where a different total is needed.
The exact per-seat allowance depends on your plan — see the pricing page for the amount your plan includes. Files in Trash still count against your quota until they're purged (see Trash and recovery), so emptying trash is the quickest way to free space.