Carbon nanotubes are interesting nanomaterials of cylindrical shapes and are structurally equivalent to a seamless folded single sheet of graphite having diameters in some tens of nanometers. They are fascinating for mechanical engineers because of their nearly highest per unit mass Young's modulus and strength. They were first synthesized by Iijima in 1991 and ever since then enormous effort was dedicated to characterize them and find their utility in engineering applications. Multiwalled Carbon nanotubes (MWCNTs) are multi-layered single wall cylinders with common axis and are more easily available. The work presented here is aimed to give an elementary exposure to the methods used by experimentalists to measure the dimensions of carbon nanotubes in all forms of single walled carbon nanotubes(SWCNTs) and MWCNTs including those that are functionalized. The use of Atomic Force Microscope (AFM) and Nanomanipulator to measure the diameter and length as well as to study the stress-strain relations is demonstrated and the results are analysed to highlight the methodology. A simple theoretical understanding of the structure of all chirality Carbon Nanotubes has also been made.