What can I use as an altar?

Having a space to use as an altar is not necessary to all
forms of magic. Here's why:

An altar is narrowly defined as a permanent or temporary
ritual place set aside for the worship a deity or deities.
This may or may not be the same as a ritual space reserved
to perform a magical spell because a given system of magic
may or may not include worship or even any contact with a
deity or deities. However, in common terms, a place reserved
to perform a magical spell is also called an altar by many
people, even if no worship takes place there.

But call it what you will -- an altar or a ritual space --
you still need a place to perform a spell, right?

Both the young and the poor may not have a space large
enough to set aside as a dedicated altar. Most people in
this situation work on top of a bureau drawer or a kitchen
table or a nightstand by the bed -- anything with a flat
surface. As with the kitchen pot that doubles as a cauldron
(see below), your work will go better if you somehow
mentally separate the furniture's use as an altar-space from
its everyday use.

In other words, your concentration and dedication to the
spell you intend to cast might benefit if you cover the
makeshift altar with a cloth (you can use a scarf or
bandana), or mark its four corners with flowers, or fan
incense smoke across the surface to clear it off before you
pout down the tools you will be using.

Likewise, when you are done, you may clear off the altar and
wipe it down with the bandana or scarf, or even clean it
with a damp cloth and furniture polish, to return it to its
"everyday" function.