This is a B note. The note B is placed on the middle line of the staff. To play the note B, pick the open second string.
Two dots placed at the end of a bar are called a repeat sign. This means that you play the song again from the start.
A black box sitting on the third line of the staff is called a half rest. It means two counts of silence. To create this silence you will need to place your pick on the open 3rd string (G note) to stop the string from sounding.
The letters above the music are called chord symbols. Do not play them now as you have not learned them yet. They are used by another musician when you play with them. Your teacher can show you how.
The small numbers at the start of each bar are called bar numbers. They are used to count the bars.