I'm new to this!

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Hello! I'm new to MFP. I'm getting married June 30 next year and would like to lose some weight! I was wondering, how does MFP work? I calculated how many calories I'm suppose to consume but when you work out it obviously changes. Are you suppose to eat those extra calories? I just want to make sure I'm doing this right since I only have 11 months!! Any advice would be awesome!!! Thanks new friends!