A carbocation has a central carbon atom with three bonded groups and one empty {p}-orbital. The geometry around the carbocation is trigonal planar because the three groups are arranged at 120$^\circ$ to minimize electron repulsion.
\[\textbf{Carbocation structure:} \quad \text{H-C$^+$-H}.\]
The trigonal planar shape is due to {sp}$^2$-hybridization of the central carbon atom.