Your internet service provider (ISP) can see that you are using a VPN, but they cannot see what you are doing with it. When you use a VPN, your internet traffic is encrypted and sent to a server controlled by the VPN provider. The ISP can see that you are connected to the VPN server, but they cannot see the contents of your internet traffic.
However, it is important to note that the VPN provider can see your internet activity. This is because your traffic is being sent through their servers. It is important to choose a reputable and trustworthy VPN provider to ensure that your online activity is kept private.