In casting, the metal is heated into liquid form and is then poured into a mould. It is then left to cool and wahla, the finished product will be in the shape of the mould.

In forging, the metal is heated to an almost molten stage and is then beaten/rolled/dropped/pressed into the desired shape. This usually requires precision tools with high pressure to work the metal.

difference between the 2 is that usually forged metal is typically stronger due to the rearrangement of the molecules by working it, whereelse in casting, the grains are more granular but bears the risk of gaps or air pockets if the process is not done right.
Think of it where a cast product is like bread but a forged product is like a cookie (more dense).
After this material choice will play a major role as well. Choose a super hard material then it'll be brittle. Choose if less brittle metal, it'll be soft.