Well its w10 mobile and i probaly could install third party apps!
It's about installing apps that are not on the marketplace. To do this, a windows phone needs to be unlocked, and for this to happen, you need an active, paid developer account, which then is linked to this phone. You'd know 100% if you've gone through those steps, so if you're not entirely sure what the whole unlocking process looks like, you probably have a normal Windows 10 mobile phone that will happily run any apps in the Windows Marketplace, but will not be able to accept apps being installed directly on the phone while bypassing the marketplace.
Again, that's no problem, it was simply an unlikely corner case I wanted to ask about. Sorry if the question was unclear on my behalf.