Quarks are fundamental particles
Quarks are fundamental particles (i.e. like electrons they are not divisible into further particles). There are 6 "flavours" - up, down, charm, strange, top and bottom. The quark model describes all hadrons in terms of combinations of quarks and antiquarks.
As an example , Protons comprise 2 up quarks and one down quark. Neutrons comprise 1 up quark and 2 down quarks.
Quarks have not been observed as a solitary particle, they can only be inferred from those of the hadrons they make up.