CH3+ is what you get when you rip an H- ion away from methane. This is not an easy task; lots of energy is needed. It can happen inside a mass spectrometer though.
This ion has one carbon atom (which brings four valence electrons with it) and three hydrogens (each of which bring one valence electron with it). This makes seven valence electrons total, however you must “remove” one because of the positive charge on the ion. This means you are left with just six valence electrons to work with.
Six electrons is just enough for three bonding pairs; this holds each of the hydrogen atoms to the carbon atom via sigma (single) bonds, and nothing else. There is no lone pair on any of the atoms here.
VSEPR Shape of CH3+ and Hybridization of Carbon in CH3+
This carbon atom needs to make three single (sigma) bonds; this implies it will have sp2 hybridization and trigonal planar geometry. The leftover, unhybridized, 2p orbital from carbon sits empty, perpendicular to the plane of the molecule. Its openness and readiness to accept a lone pair from any other particle is what makes this particle very react.