All living things are made up of one or more cells; this is one of the parts of modern cell theory. In multi-cellular organisms, cells are specialized for particular functions (jobs). This question could be answered in regards to fungi, protists, plants, and animals. I will answer in terms of animal cells; if you are interested in other types, please ask again.
Two types of animal cells are muscle cells, and nerve cells.
Muscle cells are specialized to provide movement of some sort in the animal when they contract and expand. They are generally long and thin so that when they act together and contract, they are capable of moving either voluntary muscle (such as that in a leg) or involuntary muscles (such as heart muscles or digestive tract muscles).
Nerve cells, or neurons, send messages along their length to either another nerve cell or another type of cell, such as a muscle cell. They are also long, but their structure is very different. Neurons receive a chemical signal through their branching network of dendrites. The signal is then transferred electrically along the shaft of the cell (the axon). At the other end, the cell releases its own chemical neurotransmitters that stimulate another nerve cell or other type of cell. See the attached link for a diagram; it is much easier to see how neurons structure is related to their function with a picture.
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