Well I'm trying to motivate myself to start a diet plan next week. I have no plan as far as what I will eat during my diet and dont really have a workout plan established. I am 6'2 and weight 260lbs. I'm hoping to lose about 40 to 50lbs but at the same time gain a little mass in my arms, chest and back. I'm wondering what types of exercises, diet and supplements I should be doing.

Read the sticky posts in the nutrition and exercise forums. There's a lot of information there.

I will say that you do need a plan. You can't just sort of fool around and make it up as you go along. Without a plan for both eating and exercise, you're very likely to not succeed.