Of which cells is the nervous tissue constituted? How is the generic function of this tissue related to the characteristics of the main cell type that forms it?

The nervous tissue is produced of neurons and glial cells.

The function of the nervous tissue is to receive and to transmit neural impulses (reception and transmission of information). This function justifies the characteristic morphology of neurons, with membrane projections (dendrites) to get information and an elongated membrane projection (axon, or nerve fiber) to transmit information at distance. In their turn, the glial cells support the neurons and facilitate their work (sometimes acting as insulators).

Cell Tissue - Image Diversity: neuron glial cell