When you connect to a VPN, your ISP will be able to see that you're connected to a VPN, but it won't be able to see what websites you visit or your browsing history. Your ISP will see timestamps of when you connected to the VPN, the IP address of the VPN server you're connected to and the amount of data you're transmitting. But since the actual traffic is encrypted, your ISP will only be able to see that traffic as a random string of gibberish. If you don't want your ISP to know you're using a VPN, you'll need to connect to an obfuscated server, if offered by your VPN provider.