Think about the kind of walking you will be doing. If you're spending a weekend in a muddy field at a festival, then wellies will probably be your best bet, if you're doing some light walking in a hot country, consider sandals.
Even if you want some footwear for rambling in the countryside, hills or mountains, there are some options to consider. Think about the terrain you will be encountering, will it be rocky and uneven? If so, a boot with plenty of ankle support is recommended. Do you just want footwear to keep your feet comfy when walking in the park? Then a walking shoe will probably be sufficient, many of ours are waterproof for when you're chasing after the dog through wet grass! Have a look at the Walking Boot Guide for more advice.
In the winter, ordinary wellies are quite often just not warm enough. Pick a warm snow boot or insulated wellington boot to make sure you don't get cold in those chilly months. The ground can also become perilously slippery with snow and ice. Traction aids are becoming ever more popular with people who want to use the shoes they've already got, as these studs can be stretched easily over your own shoes to make sure that you don't lose your grip!