Hello.
1. What to do with people who did not complete the survey completely, filled in half and closed, eg a browser window. Limes shows when this person has completed (and it should show when the survey is completed). How to avoid this problem.
2. I have 2 questionnaires of one person, something like an evaluation questionnaire, eg before the start of the class and after the end of the class. Is it possible in Limes to set these 2 polls to be displayed next to each other, so as not to transfer to Excel and manually compare?

1. What to do with people who did not complete the survey completely, filled in half and closed, eg a browser window. Limes shows when this person has completed (and it should show when the survey is completed). How to avoid this problem.

How can they! I would put them in prison...

Jokes aside: What do you mean exactly? "imes shows when this person has completed (and it should show when the survey is completed)."

What is the problem? That people stop answering? That Limesurvey saves incomplete responses? Please explain what they problem is.

2. I have 2 questionnaires of one person, something like an evaluation questionnaire, eg before the start of the class and after the end of the class. Is it possible in Limes to set these 2 polls to be displayed next to each other, so as not to transfer to Excel and manually compare?

No, this is not possible. Limesurvey is primarily a data collection tool, not a data analisis tool. There are some basic analisis capabilities, but they are rather basic and I don't see this changing any time soon.