A sheet is a table of records, and a field is one column of it. Fields decide what you can store, filter on, group by and chart — so the field types you pick shape everything you can do later.

Basics — Short text, Long text, Number, Checkbox.
Choices & Tags — Status, Select, Multi-select, Location, Job. Use Status for the stage a record moves through; it is what a board view groups by.
Contact & Communication — Email, Phone number, Employee, Employee List, Team, Team List. Use Employee rather than a text field for a person, so you can filter by owner and assign work.
Time & Tracking — Date, Duration, Timer. A date field is what calendar and Gantt views run on.
File & Media — File List, Document, URL.
Sheet Inter Connect — Relation, Rollup, Mirror, Formula, Link. This is how sheets stop being isolated tables.
Interactive & AI Tools — Button, Vote, Rate, AI Text.
Use a Relation field to link records in this sheet to records in another — projects to a client, tasks to a project. Once the link exists:
That is the difference between a spreadsheet and a database: one place holds the fact, everywhere else points at it.
Related: Table view · Views: see the same data 12 different ways · Field types explained