The study of skyrmions has grown as they have been realized in topologically stable spin-textured magnetic excitations. This overview treats magnetic skyrmions and skyrmion assemblies using a particle-based approach to describe a system in which the energy scales of the skyrmion-skyrmion interactions, sample disorder, temperature, and drive magnitude compete. Pinning and dynamic effects of skyrmions interacting with disordered or ordered substrates are of technological importance for skyrmion applications. Analogs to vortices in type-II superconductors, charge density waves, and colloidal particles are presented.