Props (blocks, bolsters, straps) are helpful, not mandatory — and household substitutes cover most of what a beginner actually needs.
What props actually do
A block extends your reach in standing poses; a bolster or rolled blanket adds support in restorative poses; a strap extends your reach in seated stretches — all three exist to bring a pose within comfortable range, not to make it 'more advanced.'
Household substitutes
Thick books stand in for blocks, a rolled towel or firm pillow substitutes for a bolster, and a bathrobe tie or long scarf works as a strap — genuinely functional substitutes for someone just starting out.
When dedicated props are worth it
If a gentle practice becomes a regular, long-term habit, proper props (particularly a stable yoga block and a supportive bolster) do offer more consistent support than makeshift substitutes — worth considering once the habit is established, not before.
Is a yoga mat necessary?
Not strictly — a carpeted floor or a folded blanket provides enough grip and cushioning for most gentle, back-focused poses; a mat becomes more valuable for standing or balancing poses on a hard, slippery floor.