Gravity is the weakest of all the four forces but has the longest range. It is
always an attractive force between two objects in the Universe.
The Weak Nuclear Force, as its name suggests, is weak and has a short range. It is
responsible for radioactive decay and neutrino interactions.
Electromagnetism has a long-range and can be attractive or repulsive. However, it
only acts on objects carrying an electric charge. It is responsible for the attraction and
repulsion of unlike and like electric charges or bar magnets.
The Strong Nuclear Force, as its name suggests, is strong but has a short
range. It is an attractive force but can be repulsive. It is responsible for holding the nuclei
of atoms together.
It is believed that at very high temperatures, such as those in the Big Bang, all the four forces
unify to form a Combined Force. As temperatures lower, the forces separate in a process
known as Spontaneous Symmetry Breaking.