Working on a human character and when i try to add faces to attach the body it wouldn't work .. Tried F , Alt + F. Relatively new to blender.
Are they two separate objects or one? The meshes need to be one object before you can join faces. Once they are a single object, selecting the same number of parallel edges should allow you to fill the empty face. If that doesn't work, take a full-screen snapshot or possibly upload your file.
You have overlapping vertices as can be seen from black dots with orange rods. Press A in Edit Mode to select all vertices and from Mesh drop down (or pop-up) menu select Clean Up > Merge by Distance.
You can also select vertices and press F3 and search Merge by Distance.
Next try filling again.