The space between notes is called a semi tonea to a flat is a semitone, a to b is a full tone. the dashes represent divisions of the tone or semitone. The gap in a full tone is 200 cents, in a semitone its 100 cents therefore each dash represents five cents, so if you are 1 dash out you are either flat or sharp by 5 per cent of one semi tone. believe it or not, goood violinists can quite plainly here if you are five cents out, soloists have to be perfec, and thats what everyone who plays violin should aim for, which is why ear training is so important..as well as practising intonation. You can have superb tone but sound terrible if you are slightly flat. There are cases when you play notes sharp on purpose, this is generally in pythagorean tuning, for instance you would shorten the interval between c sharp and d. If you were playing with different instruments you play in tune with them. Andrew could answer this question a lot better than I can it can be quiet complicated, I have said before all violinists struggle with intonation and practice it all the time, its  one of the main reasons violin is so difficult, I myself struggle getting the note b perfect, (as well as all the others,)