If you want to encrypt something with RSA in C# you could use the RSA class: http://msdn.microsoft.com/en-us/library/system.security.cryptography.rsa(v=vs.110).aspx
Asymmetric cryptography is just a pair of keys for decrypting/encrypting. You just choose one of them to be private and the other one to be public. If you encrypt using one of them the decryption should be done with the other one.