Your team needs to agree on what story points mean. As long as they make sense relating to each other.
So maybe 1 is change a label, 2 is write a back end api, 3 is add a table to a screen with corresponding data and 5 is solve a problem you don't fully understand yet. As long as you make reference points with your team, you'll be able to calculate your velocity and the size to stories to each other.
Yes. I have a table that I go over with new people. Also, we make frequent references to our baseline at sprint planning. So we will say things like "that's 5 story points because there's a lot of uncertainty about how to do it" or "that's 2 story points because it always is" (we have some recurring tasks)