A solid has a definite, rigid shape and a definite volume, which does not change significantly with change in temperature or pressure. So placing a solid into a container the solid does not move because the particles are in a fixed location. There is very little space between the atoms or molecules in a solid so solids are incompressible.

Solids can be pure substances or mixtures. Most solids are mixtures, and most of these mixtures are heterogeneous.

What does a solid look like at the atomic level?

The atoms or molecules of a solid are very ordered, very close to each other and move very little.