Kenny, keep a food diary including portion sizes, and record your before and after levels alongside. That is the way to learn.
Test immediately before you eat (after washing hands and drying thoroughly) then test again 2 hours after your first bite. Keep an eye on the actual rise from before to after. Initially this should be less than 2mmol/l. Eventually you will want to lower this target and start testing at other times between eating and the 2 hour mark. Slowly but surely, you will get there.