It all depends on what kind of electric ukulele you’ve bought. There are two main types: the acoustic-electric and the electric. The acoustic-electric can be used without an amp as this alternative features a hollow body that will allow for sound to resonate without the need for other devices.
The electric option, on the other hand, has a solid body which means that for sound to be played, an amplifier is absolutely necessary. With the lack of a hollow body, a pickup is necessary. The pickup will respond to the vibrations of the strings and transfer these waves in the form of electricity to the amplifier which can then transform those waves into sound.