boyles law states that
For a fixed amount of gas at constant temperature, the pressure of the gas is inversely proportional to its volume.
this means that:
$$ P\times V= \text{Constant}\\ p\propto\frac{1}{V}\\ V\propto\frac{1}{p} $$
it is using this understanding that we can show that the compression of a gas leads to an increase in pressure visa versa.
this only holds true at a constant temperature and so this leads to the creation of p-V isotherms.
an isotherm is the relationship between the pressure and volume at different temperatures. as the temperature is increases the same volume of gas will exert larger pressure
