Question
Hello, My backyard is sorta on a slope on one side, and at the lowest point the water pools badly after raining.
Do I dig at the lowest point a few feet and insert sand and gravel or do it scale back from the slope and try to fill up the lowest point, so its more level with the slope.

Answer
The drainage problem appears to be topographical; that is, the slope does not continue past your backyard. Altering that may affect the adjoining property in that the water will then drain on to it. I am not competent to advise you about this aspect. You can do the 'gravel thing' which will cause the water to drain downward into the soil profile. But I would recommend that you dig down with a post hole digger first to determine how deep you will have to go to get the internal drainage you are trying to achieve. What you are trying to do is not complicated but it can get so. Proceed with caution.