The Employment Relations Act sets out the basic legal framework for things such as negotiating and entering into employment agreements, belonging to a union, going on strike, and resolving employment problems (see the chapter “Resolving employment problems”).
Other Acts set out minimum conditions that apply to all employees (although you’re also free to negotiate better conditions with your employer). For example, the Holidays Act 2003 sets out your minimum rights to annual leave, public (“statutory”) holidays, sick leave and bereavement leave, while minimum wage rates are provided for by the Minimum Wage Act 1983 (see the chapter “Employment conditions and protections”).
Other Acts give you minimum protections in certain areas. For example, the Health and Safety at Work Act 2015 requires your employer to provide a safe workplace, while the Human Rights Act 1993 requires employers to treat all employees equally, regardless of factors such as race, gender and marital status (see the chapter “Discrimination”).