The main part of tantra is sadhana, or union with a particular deity. This union is achieved through identifying with the body, speech, and mind of that deity.
The adept envisions the chosen deity in their mind, and then repeats particular mantras designed to invoke that deity until it arises in the individual worshiper.
To this end, one also uses mudras (hand gestures) and even a mandala (sacred diagram) that call forth that tantric deity.
Initiation by a religious teacher (a ceremony known as abhishekha) is necessary to embark on this sadhana of union with the divine.