I have an area of about 40' x 60' that is shaded by a couple large maple trees. Also, most of this area is extremely wet in the spring time, or when we have a lot of rain through the summer. In fact, I often have standing water over much of the area.
How Do I Grow Grass in Problem Area?
Certified GKH Gardening Expert
It is likely that grass will not grow in those conditions. I would consider creating a rain garden to help drain off the standing water (https://www.gardeningknowhow.com/special/spaces/rain-garden-design.htm) and then once the area is drier, plant a shade tolerant grass (https://www.gardeningknowhow.com/lawn-care/lgen/shade-tolerant-grass.htm)
Tile area first to promote proper drainage, next make sure that your problem isn't from shallow root system from your trees depriving grass of vital nutrients.
If your trees are the problem than you probably will not be able to grow grass without removal or thinning of your trees to allow sunlight in.
If this is not an option have a soil test done to determine PH
Plant a shade tolerant grass