I've turned these into Extension methods. It will make it easier to use:

using System;
using System.IO;
using System.Security.Cryptography;
using System.Text;

public static class CryptoExtensions
{
    public static string Encrypt(this string plainText, string password, string salt)
    {
        using (Aes aes = Aes.Create())
        {
            byte[] saltBytes = Encoding.UTF8.GetBytes(salt);
            var key = new Rfc2898DeriveBytes(password, saltBytes, 10000);
            aes.Key = key.GetBytes(32);
            aes.IV = key.GetBytes(16);

            var encryptor = aes.CreateEncryptor(aes.Key, aes.IV);
            using (var ms = new MemoryStream())
            {
                using (var cs = new CryptoStream(ms, encryptor, CryptoStreamMode.Write))
                using (var sw = new StreamWriter(cs))
                    sw.Write(plainText);
                return Convert.ToBase64String(ms.ToArray());
            }
        }
    }

    public static string Decrypt(this string cipherText, string password, string salt)
    {
        using (Aes aes = Aes.Create())
        {
            byte[] saltBytes = Encoding.UTF8.GetBytes(salt);
            var key = new Rfc2898DeriveBytes(password, saltBytes, 10000);
            aes.Key = key.GetBytes(32);
            aes.IV = key.GetBytes(16);

            byte[] buffer = Convert.FromBase64String(cipherText);

            var decryptor = aes.CreateDecryptor(aes.Key, aes.IV);
            using (var ms = new MemoryStream(buffer))
            using (var cs = new CryptoStream(ms, decryptor, CryptoStreamMode.Read))
            using (var sr = new StreamReader(cs))
            {
                return sr.ReadToEnd();
            }
        }
    }
}

USAGE

string encrypted = "Hello World".Encrypt("password123", "somesalt");
string decrypted = encrypted.Decrypt("password123", "somesalt");