You need an adaptor ring..... as you only mention one lens, you need the 82mm size.
You then need a 'filter holder' - the bit that slides onto the adaptor ring and holds filters.
As a 'starter kit' (and I think you'll find starter kits in most big photographic shops), I'd recommend a Circular Polarising Filter (CPL), a Graduated Neutral Density filter - "ND6 soft Grad" is a good start. After that, you'll be able to decide where to go from there. Most people get some extra ND Grads, with different strengths and/or different amounts of graduation (soft, hard, medium).
Cokin is the most common brand that you'll see in shops but they're not top quality - if you're serious about filters,
Lee Filters are better quality and they make a starter kit.