Pick a plant to see what it grows well beside and what to keep it away from. Pairings are the classic, widely-published ones, a mix of tradition and trial, so treat them as guidance for arranging your beds.
Companion Planting Guide is a paid tool
It's part of the Homeowner / Gardener plan ($3/mo). Commercial accounts include it too.
Companion planting mixes solid science (trap crops, scent masking, pollinator draws, nitrogen fixing) with garden lore. Use it to arrange beds and rotate families, but your own results and local pests are the final word.