What is the role of mesons in nuclear forces?
Mesons are what are called propagators of nuclear force.
Mesons are what are called exchange particles. Nuclear force is experienced by exchange of mesons inside the nucleus. This was first hypothesized by Yukawa to explain the short range of nuclear forces.
But today we have replaced Yukawa's Meson theory with Gellman's Quark theory , mesons play no role in nuclear force, it is Gluons which carry nuclear force and protons and neutrons inside nucleus are themselves composed of quarks . But Mesons are a very good approximate to explain a lot of nuclear properties.