According to the theory of comparative advantage what tasks should one perform and what tasks should one purchase from others?
We generally talk about comparative advantage with reference to countries rather than individuals, but individuals could be used to illustrate this theory as well.
If Person A has a lower opportunity cost for making a good than Person B, Person A has a comparative advantage in terms of that good. Person A should make that good and Person B should buy it from him/her.
The reason for this is that it is in Person B's best interests to buy that good from Person A even if Person B could make it him/her self. If Person B buys this good from Person A, B can use the time and resources she saved (by not making the good) to make something that is more valuable. Person B could then sell that more valuable good to Person A and both will be better off.
To fully understand this, it is really useful to look at a chart showing opportunity costs for different people and different goods. You can click here to find such a chart.