If you do not have to leave home then you should consider your options very carefully before doing so. If you are not at risk of harm where you live then you may not be entitled to help from the Council. If you have not planned your move you may also not have money for the deposit and rent in advance you often need to secure private rented accommodation
If you are at risk of harm you should seek help immediately and will be offer support.
Some 18 to 21 year olds claiming Universal Credit are not entitled to help with housing costs.
The GOV.UK website provides more information about which 18-21 year olds can still get help with their housing costs.