ive heard that it all matters on how many calories you eat in one day

to determine if you would gain weight......what if a 5'11 male 205 lbs eats 2000 calories but with 175 grams of fat, wouldnt that gain weight?

Since each gram of fat contains nine calories, if someone ate 175 grams of fat they would be getting 1575 calories from fat.  If they only ate 2000 calories per day, they would be getting 79% of their calories from fat, and personally I think that would be very difficult if not impossible to do.  But theoretically, as long as they burned as many calories as they ate, no, they would not gain weight.

Calories determine weight but dietary balance determines health.  The 5'11" male etc., could probably eat 2000 calories of chocolate chip cookies and french fries a day and probably not gain weight but would look pretty sickly in a short space of time because they wouldn't be getting the full range of nutrition. 

A moderately active young male, 5'11" and 205lbs should be able to maintain their weight between 2800-3500 a day.  Fats should comprise no more than 30% of the total.