Maria, on the top right hand corner, there is a "Find" button to click on. You can look up a surname there to see if your ancestor is already listed ("has a profile"). Or maybe one of the parents or other ancestors already has a profile. When looking for a specific person in a surname on a long list of profiles, you can sort the list out by birthdates to make it easier to find that person. (Where it says "Click on name to resort")
I looked up "Rochette" on the surname find, and there are a lot there already, but it doesn't look like any from 1765. There may be many of the other surnames already there too.
http://www.wikitree.com/index.php?title=
Special:Surname&s=ROCHETTE&order=dobup&u=
Most of these are "open profiles", (a black and white open padlock is the symbol for open profile), meaning that, if you have something new to add to that profile, you can go up to "Edit" when you are on that profile and add it, including siblings, parents, spouse, etc. Or you can click on "Send private message" to contact the profile manager (who looks after this specific profile) and suggest the addition or change. This sends an email to the profile manager.
If these profiles are not part of your family, you can start adding your family. Here are good directions:
http://www.wikitree.com/wiki/Adding_Family
There are many who can help if you get stuck. You can click on the "help" button if needed, but also you should make use of the help the greeter here can give you.
Add WikiTree to your "favorites" list to find the page you want quickly next time.