composition delar has to issue Bill of Supply .As per rule 49 of CGST rules 2017 . Fromat for bill of supply given bellow .
He must mention on the bill of supply" composition Taxable person not eligiable to collect tax on supply "
1) Name and address , GSTN no of supplier
2) A consecutive serial number not exceeding 16 characters , in one or multiple series , containing alphabets or numbers or special characters-hyphen or dash and slash symbilised as "_" "/" respectively , and any combination thereof , unique for the financial year
3) Date of issue
4) Name , address , GSTN no of recipient if he is registered .
5) HSN/SAC code
6) Discripttion of the Goods
7)value of supply taking in to account discount
8) Signature or digital signature
You have record all sales Invoice in books .
you must keep other record such as purchase invoice ,payment , receipt , credit note , debit note , delivery challan , stock , Out put tax payable , Advance payment , Godown , transporter , etc .