what kind of certificate needed for my application ?

Question

I am releasing free C# softwares I've created using Visual Studio. In the future, some of these softwares might become Paid. I was wondering if I need to purchase any kind of license for them ?

I understand that it's good to have a certificate for your website (SSL?), if your trying to sell your software but what about your applications ?

I just don't want anti-virus/browsers flagging my application as not trusted. Any suggestion is appreciated.