Vinaigrette sauce is a classical sauce mostly used in salads. It is a combination of oil (usually extra virgin olive oil) and vinegar. The ration is usually 3 tbs of oil : 1 tbs of strong vinegar.
When making this sauce chefs usually firstly put salt in vinegar and mix till the salt melts and that they add olive oil. You can also add pepper and other spices depending on what you like.
Here is one version of this sauce
Walnut vinaigrette sauce
Mix oil, vinegar and salt in the mentioned ratios. Add 1 tbs of finely chopped walnuts, 1 tbs of chive and a bit of black pepper.
You can add all kinds of spices in the basic sauce like: mustard, parsley, orange, garlic…