Basic French vinaigrette is oil & vinegar (3:1) and salt. Salt to taste.
3 parts fine virgin olive oil
1 part vinegar (red or white wine vinegar)
Rapidly whisk vinegar and salt (if possible, use sea salt or ground rock salt so it will dissolve a bit.) Add oil in a stream so it will emulsify.
Variations: Use lemon juice instead of vinegar. Use balsamic vinegar. Substitute any mild oil. Add capers, or fresh herbs such as: tarragon, thyme, basil, shallots, onions Add sugar.
Whatever seems interesting to you.