Most instruments have small variations in the tuning for each note compared with a “perfectly” tuned piano for example. Each instrument, not just each type of instrument, will have some notes that are a little sharp or flat compared to each other. As you get more experienced playing your instrument, you will find yourself naturally correcting the tuning, perhaps without realising it. In fact, when you play with other people, being able to listen to them and adjust your own tuning to match is one of the essential skill of ensemble playing.
You can get a better idea of how your own instrument varies in pitch for each note, by using a tuner app (like Timbre) to see if the notes are typically sharp or flat for some notes.
One of the things that Timbre makes clearer is that for some intervals (e.g. a 3rd), one of the harmonics of a different note could be a little bit different to an equal tempered 3rd and needs to be adjusted a little to match the harmonics of other instruments, for example.