10 weeks to get in some sort of shape!

What is your age, current weight, height and what would you be looking to get down to? Male or female?

Joining the gym is a step forward (not necessarily vital as there are plenty of other types of training you could do) but as anyone will tell you around here, it's ALL about getting your diet tidied up. As in, 80-90% about what you eat, 10-20% about gym/exercise.

Post up what you'd eat on a typical day (and be honest!)
How many calories do you consume a day and are you familiar with calculating your TDEE?

If you could post up answers to all the above, you'll get more specific info on what you need to do but from a general point if view, cutting out processed food, take-aways, booze, choc/crisps, white bread and fizzy drinks will help.
Up your intake of good fats and protein (avocado, nuts, eggs, lean meat, chicken, turkey, fish, plenty of veg/greens). Plenty of water too, 3-4l a day.
Watch your portion sizes, weigh your food and track what you're eating on an app like myfitnesspal.