Resistance is a measure of opposition to the flow of current.

Here is an analogy to represent this, it is water flowing through a hose pipe, but it has been squeezed. The flow of water out of the end is less because the squeeze is resisting the flow of water. This is analogous to how resistance opposes the flow of current:

All components have resistance, so by adding more components to a circuit, you increase the resistance of it.

If you have a bulb in a circuit, the bulb provides resistance. If you add more bulbs, you are also adding more resistance.