Certificate public key keyexchange, Which key exchange is used in browsers?
The RSA encryption algorithm implies two types of keys: a public key and a private key. The public key is composed from the public exponent $e$ and modulus $n$. The private key is composed from the private exponent $d$ and modulus $n$. The relationship between them is $(e,d)\ ≡\ 1\ (mod\ φ(n))$. To encrypt, you rise the plaintext to the power $e$ and to decrypt you rise the ciphertext to the power $d$ (both operations are done modulo $n$). More detalis here. The traffic between you and StackExchange is encrypted under the TLS protocol. The TLS protocol uses a hybrid encryption scheme. That is, you first generate a random key, say K, that you'll encrypt with RSA using the public key of StackExchange. The StackExchange will decrypt the key K using its private key. 
From now on you will both use a symmetric algorithm (AES 256) to encrypt your data. The encryption key for this symmetric algorithm will be the K key, which you previously encrypted using RSA. More detils about TLS here.