Try using this basic calorie calculator - it should give you a rough estimate of how many calories you need to maintain your weight, and how many you would need to consume to lose weight:
If you want to lose 10k I am guessing you mean 10k of fat, because in order to become muscular you would need to gain weight at some point or another.
For fat loss try and focus your routine on cardio e.g. running, bike, rowing, swimming etc. It's not a bad idea to do some lifting too. If you're just starting out then try to take it easy, but keep it consistent and think about the long-term i.e. it's not just about losing that 10k.
Most importantly is diet. If you don't eat right, or don't drink enough liquids, you will seriously compromise your workouts and will not really see any results. Keep your diet as clean as you can with lean proteins e.g. chicken, Turkey, Fish, Beef as well as plenty of fruit and veg. Avoid highly processed foods, and foods with too much saturated fat, sugar, salt, additives, preservatives. When you think about it, it is pretty straightforward. Just eat healthy, with the odd treat now and then ...