setting game to play offline

What game are you trying to play offline? @Vinny has the link that has the information you need on using your console offline, and what to expect when doing so, but there are some games that still require an internet connection that aren't necessarily
fully online games. If you let us know which one's you're trying to play, we can help let you know if being online is a requirement.

Once your device is set up, you’ll need to launch each game you want to play offline while signed in to Xbox Live. You only need to do this once per game, and you’ll need to do this even if you’ve already
launched the game on your device. 1. Make sure that you’re online, and that your device is set as your designated offline device. (See the steps above for details on how to do this.) 2. Launch the game you want to play offline. When prompted, sign in to Xbox
Live with your account. 3. Once you’ve started playing the game, you can exit at any time. Repeat this process for each game you want to play offline. Once completed, you can go offline at any time and launch those games whenever you want to play them, without
needing to sign in online each time.

This is what I found hope it helps. Happy gaming!

I dont know how to download games

The following instructions can be useful: https://beta.support.xbox.com/help/Hardware-Network/connect-network/using-xbox-one-offline

Keep in mind that some games require constant online connection to work.

You need to open the guide, go to settings and network settings and select go offline.

Any games that can be played offline will be playable. You would need to check which of your games can be played offline.