Within the Yasawas, the Yasawa Flyer is the main public transport. If you are island-hopping, you ride it between your stops. Most resorts arrange their own boat transfers from the Flyer for guests — the catamaran anchors offshore and resort dinghies come out to collect people.
Between islands that don't have a scheduled stop, or for reaching beaches and villages on the same island, you rely on whatever boat the resort or guesthouse can arrange. For budget travellers staying in village bures or backpacker resorts, informal arrangements with local fishermen or resort staff are usually possible. Confirm details and negotiate a price before you commit.
Walking is practical on most islands along the main track, but the terrain is hilly and the heat demanding — take water and go early in the morning or late in the afternoon. There are no roads as such; what tracks exist connect villages and resort buildings rather than making a circuit of the island.
Kayaking is offered by most resorts and is a good way to explore coves and reefs close to shore. Standalone resorts also offer snorkelling gear hire, so it is worth asking what is included in your accommodation.