The website you mentioned does not appear to be legitimate, do not enter any info in there (I removed the link for that reason).
To know where to lodge an application, you need to track down the local French consulate (or embassy's consular section). Unfortunately, I could not find an official list on the Foreign Ministry's website but French embassies have domain names starting with “ambafrance” like ambafrance-us.org or ambafrance-nl.org. Consulates use a similar format starting with “consulfrance” followed by the name of the city, e.g. consulfrance-kyoto.org.
Sometimes you will have to apply through a third-party provider like TLScontact but you should follow the link on the consulate's website to make sure you are not landing on some scam website. Similarly, if you need to use an agent, you have to make sure they are trustworthy because many are just trying to pocket your money without actually applying on your behalf.
Unlike the website you found, the official form does let you apply for a single or two-entry visa and that's what you should do if you can only provide documentation regarding one journey. You won't get a multiple-entry visa simply because you ask for it, especially if that's your first application.