If your landlord is slow making repairs to your home you should formally write to them to request they make the repairs (in a letter or by email). If they don't do the repairs you can get advice from the Council Private Housing Standards Team.
The team can also give advice on the tenancy law and offences, and on their law and rights advice webpage they advise on eviction by landlord, harassment by landlord and ending a tenancy.
If your landlord has served you a notice you can contact the Council Tenancy Relations Service for advice. Not all notices served are valid and the team can check that for you.
Sheffield Shelter has a city centre drop in where you can get advice on a range of housing issues including problems with your landlord like delays with repairs and harassment. More details below.