Transmission wont pull in forward gears. its

I feel it go in gear but it's like you jam on brakes and instantly stop.

Honestly there’s probably not enough fluid out into it. When you fill it and you think it’s full, it’s more than likely not. When the car is running and is warm check the trans level. Must be warm and running. You slosh around the fluid and it fills the torque converter and other parts of the transmission so when its sitting there its a false reading on if its full or not