I have been told there is no point in applying until I get my grades - is that right?

No that is not correct. You should be applying for post-16 opportunities early in year 11. Colleges and 6th Forms will give you a conditional offer. This offer will tell you what grades you need to get onto that particular course. Most colleges are able to offer you an alternative course if you do not get the required grades. If you are in year 11 and have not already applied for any courses do so NOW!