As its an island, there are really only two ways to get to Bali: by air or by sea.

Bali by Sea
The main sea route is by ferry from the eastern tip of Java. Ferries leave Ketapang on Java every 15 to 30 minutes, 24 hours a day.

Bali By Air
If traveling by air, your point of entry and exit is the Ngurah Rai international airport of Denpasar. Many international airlines have daily flights to and from Bali. The airport is also well connected to the rest of Indonesia by the country's half-dozen domestic carriers.

If connecting between domestic and international flights, note that the connection will involve getting from one terminal to another, which requires a short 10 to 15 minute walk.