The antenna you want depends on your application. To start with, there are two classes of antenna: omnidirectional (where the signal radiates out from the antenna with equal strength regardless of the angle you are from the antenna feed point) and directional (where the signal is stronger in one direction than in other directions). If you have a fixed transmitter and a fixed receiver, then you'd want directional antennas pointed at each other. If you have a moving receiver or transmitter, then omnidirectional antennas will be easier.
After that, antennas have orientations: they can be horizontally polarized, vertically polarized, or circularly polarized. In general if one antenna is horizontally polarized and the other is vertically polarized, you'll get signal loss.
A half-wave dipole is a simple antenna. It consists of two equal lengths of wire, each 1/4 wavelength long (approx; start a little longer because wire is not a perfect conductor). One wire is connected to a coax centre conductor and the other connected to the braid. Here's a picture