An altar is not an essential thing to have. It depends on how you feel as there is no right or wrong answer to this.
I have one but rarely use it in spells. I find that it just gets in the way in the circle. It doesn't have to have expensive or bought things on it either. A cangle to represent fire, a stick of incense for Air, a bit of sand/salt/dirt/or a crystal for earth and water in a container for water. These are the basic things.
Next you could add a God or Goddess statue, wand, athame, crystals, stones, tarot cads, runes etc.
It is up to you on what you want.