Every grid in the app (Projects, Companies, People, Employees, and more) can show a different set of columns than the default — this is a personal preference, saved per user, not something that changes what anyone else sees.
Every grid's toolbar has a Choose Columns button, right alongside Show Filters, Print List, Export to Excel, and Reset Columns.
Two lists side by side — Available (not currently shown) and Selected (currently shown as columns). Drag a field across, or select it and use the toolbar buttons:
Once a field is in the Selected list, use Move Up / Move Down to change its position — that's the actual left-to-right order the columns will appear in on the real grid.
On entities with a lot of related fields, they're organized into named groups (e.g. every "Markup" field on an Estimate). If groups exist for that entity, buttons appear above the two lists — Show [Group] / Hide [Group] — to move a whole family of fields in one click instead of dragging each one individually.
Click Save. This is saved per user — it changes what you see on that grid, not what your coworkers see.
Use the separate Reset Columns button (next to Choose Columns on every grid's toolbar) — it's a different fix for a different problem: it clears a corrupted saved column width/order, not your column selection itself. If a grid's columns look stuck, squished, or in a broken order after a browser update or similar, try this before touching Choose Columns.