Hypothesis Testing. Power Function

We just learned this today so I am just slightly confused on how this stuff works. Any hints or starters would be great!! Thank you!!

Suppose the proportion p of defective items in a large population of items is unknown and that it is desired to test the following hypothesis:

Null: p=.2, Alternative: p does not equal .2

Suppose also that a random sample of 20 items is drawn from the population. Let Y denote the number of defective items in the sample, and consider a test procedure delta such that the critical region contains all the outcomes for which either Y is greater than or equal to 7, or Y is less than or equal to 1.

Determine the value of the power function at the points p= 0, .1, .2, .3, .4, .5, .6, .7, .8, .9, and 1 and sketch the power function.

Determine the size of the test.