You can play against the computer on lichess.org for free and without registration by following these steps:
- Step 1: goto lichess.org and click on PLAY WITH THE COMPUTER.
- Step 2: choose the computer strength. If you are beginning at chess, playing against level 1 will be a very good way to see if you can beat an opponent who makes some obvious mistakes
- Step 3: choose the color you want to play with: white, black or random.
As you can see on the screen capture, you can also choose a different chess variant and fix a limited time control.
Step 4: that’s all, you can start to play !
As you can see, playing against the computer without registering is very simple on Lichess!