The first 20 elements, in the tableTap an element · see why it sits there
Every ring on the diagram is a shell. The number of shells is the period.
Groups 1 and 2: the group number is the number of outer electrons.
Helium is the exception: its outer shell is full with just 2, so it sits in Group 18 with the noble gases.
Hydrogen is a non-metal even though it sits in Group 1. Boron and silicon are semi-metals: they act a little like both, and the booklet says not to worry about them yet.