The chamber is actually just a beaker large enough to house the TLC plate without having to bend the plate. Just enough developing solvent (discussed on the TLC page) is placed in the beaker to cover the bottom. The solvent level must be lower than the origin of the TLC plage (about 1 cm) otherwise the compounds that had been 'spotted' onto the origin could dissolve in the solvent. Usually a piece of folded filter paper is also placed in the beaker and wetted with the solvent. This saturates the air in the developing chamber with solvent molecules. A watch glas is placed over the beaker to prevent evaporation. Remember to leave the chamber undisturbed after the TLC plate has been placed.
After developing the TLC plate, mark the solvent front, calculate the Rf values, and dispose of the developing solvent properly.