To create a wallet account, the first is login and open your email, very many sites that offer online wallet services, you can start with bittrex, poloniex, localbitcoins and others. Choose one of the wallets that you like and visit the site, then click REGISTER, and follow the next command, hopefully useful.
OP is asking about how to create a wallet app from scratch not creating a wallet account.
I think you will find many online tutorials that will help you build your wallet. And since you are a c# developer it is not going to be hard because you will find a lot of libraries that you can use.
I hope you will find some useful information here:
https://www.codeproject.com/Articles/1115639/Build-your-own-Bitcoin-walletI will come back later with more links.
