Getting to Cabinda requires some planning. As an exclave separated from the rest of Angola by a strip of the Democratic Republic of Congo, there are no road options that stay in Angolan territory.
By air is the most practical approach. TAAG Angola Airlines operates flights between Luanda and Cabinda (Coronel António Agostinho Neto Airport), typically several times a week. The flight takes under an hour. Book well in advance as seats sell out — the route is used heavily by oil industry workers.
By sea, small boats occasionally make the crossing from Luanda or from DRC ports, but this is unreliable and not recommended for independent travellers.
Overland through DRC is theoretically possible but requires separate Congolese visas, involves crossing two border posts, and is logistically complex. Unless you are entering from the DRC for other reasons, flying is by far the better option.