Most objects are electrically neutral. This means that they have an equal positive and negative charge, each canceling the other out. In order to charge an object you have to alter the balance of negative and positive one way or the other. There are three ways to do this.
There are three ways to charge an object: friction, conduction and induction. Friction involves rubbing on material with another, resulting in electrons moving from one surface to another. Most people have experimented with this form of charging an object, either rubbing a balloon on a jumper to make it cling or by shuffling their feet over a carpeted surface to build up an electrical charge to shock someone. Friction is useful for charging insulators, which are materials that aren't good conductors. Conduction on the other hand is used to charge things that are good conductors, such a metal. A charged object is touched to the conductive material and some of the charge, whether it is positive or negative, will be transferred. The final way to charge an object is by induction and is, again, best for conductive materials. The uncharged conductive material is grounded on any neutrally-charged material and the charged object is held near it. The charge will flow between the two objects and the uncharged conductor will develop an opposite charge to the original charged object.
Insulators and Conductors
There are three different types of material: conductors, insulators and semi-conductors. Insulators consist of woods, rubbers and plastics, materials along which charge does not flow easily. This is why leads that plug into the wall have a rubber sheath. Conductors, such as metal, allow the charge to flow from one end to the other easily. Semi-conductors are a useful intermediate and can be manipulated using measured impurities that alter just how conductive the material is.
The SI unit of measurement used for electrical charge are coulombs, named after French physicist Charles-Augustin de Coulomb. Charles-Augustin de Coulomb also developed Coulomb's Law which measures the electrostatic force of attraction/repulsion between two objects.
It is easy to experiment with the process of frictional charging. Most people will already have experimented with charging a balloon by rubbing it on their jumper. Once the balloon is charged it will cling to similarly charged objects or lift someone's hair towards the charged rubber surface. Another experiment is to take a plastic pen and rub it hard with paper. Once the object is charged it can be tested using a kitchen tap since if you turn the tap on the charged pen will attract the flow of water.
Cold weather makes it easier for an object to build up an electrostatic charge. This is because cold air is drier than warm air and electricity is unable to discharge as easily.