Altars can be found in any place you practice spiritual worship. This could be a shrine, temple, church or a place in your home that you set aside so you can manifest and fill your home with comfort. The altar doesn't need much on it, but you should be mindful of the items you place on your altar to celebrate all that you are.
Clear a space in your home that you will see daily. Remove any clutter or items that will not be a part of your altar. Clear any negative energy that may be lingering in the space with incense and sage. (Please source your sage responsibly, as white sage is sacred to the Natives of North America and there are concerns it is being over harvested and won't survive.)
Once all this is complete, you will pick a theme for your altar. Your altar should align with your purpose, interests or goals. Add items that you feel personally connected to, to your altar. Take your time. You can add bits and pieces as you go or set aside a specific day for this. Get creative and use lots of color, crystals, candles, flowers, personal trinkets or treasures, incense, smudges, photos or quotes that bring you positive energy. It is highly recommended to include items that represent the four elements.
For example:
Earth for grounding: sage, botanical smudges, crystals
Air for action, ideas and motion: incense
Fire for passion: candles
Water for intuition: a bowl or cup of water
There is no right or wrong way to setup an altar, so don't get hung up on how other people may or may not have set up their altar. Arrange your items in a way that feels natural to you, and makes it easy to access items you can hold during prayer or meditation. Full moons are a great time to arrange your altar for setting new intentions. As always keep your altar clean, dust free and maintained. Even when you are not using your altar it still holds energy.