Amperes are a measure of how much electricity is flowing through a circuit. It's important to understand that amps are the result of a fixed voltage (force) pushing on a circuit of fixed resistance. For electricity to flow, there has to be a path from that source of high potential energy to ground (a point of very low electrical potential). If we have a pressure of 120 volts and a huge resistance, there will be no electrical current flowing and no amps measurable. We call this an open circuit. If the resistance is lowered (for example, by closing a switch), then electricity can flow through the circuit to ground. The amount of resistance that the electricity encounters will determine how much current flows. The larger the resistor, the smaller the flow. The smaller the resistance, the larger the flow.
If there is no resistor in the circuit, there will be very little resistance and tremendous flow. Electricians talk about this as a short circuit. This should blow a fuse or trip a breaker.
Too much electrical flow is a bad thing because wires will overheat and melt. If the resistors are sized appropriately and the current flow is what we wanted, light bulbs will glow, but will not melt, heating elements will give off heat but not break apart, and electric motors will turn but not overheat.