Just mix everything up together until it is all blended and the oil has emulsified into the yoghurt/sour cream. Taste for seasoning, and add salt if you think necessary. Put in a resealable container.
Allow to 'sit' in the refrigerator for at least 2-3 hours before using to allow the flavors to come out.
This wonderful meze (we do not think of it as a sauce here- it is a thick 'salata') is used to counterpoint rich, bbq'd meats (like souvlaki/shish kebab), but can be used in more diverse ways.
Place a small plate full on your dinner table for people to scoop up small amounts onto their bread (preferably crisp-baked pita).
Fry up some zucchini or eggplant slices (dredge in flour and fried in olive oil) and serve with a dollop of tzatziki on top.
Use as a salad dressing.
A dip for crudites.
Note: If I have time, I often lightly salt the grated cucumber and put in a colander to drain, then squeeze out water as per usual. This eliminates even more water.