Read it again any time, including while you work through the exercises.
Open a pair of scissors: the wider you open it, the bigger the angle between the two blades. An angle is exactly that: the opening between two rays starting from the same point, the vertex. Careful, the length of the blades does not matter! Small scissors opened wide make a bigger angle than long scissors barely open.
To measure an angle, we use a protractor, graduated in degrees (°). The reference to know by heart: a right angle measures 90°, like the corner of a sheet of paper. An angle more closed than a right angle (less than 90°) is acute, like an arrowhead. An angle more open (between 90° and 180°) is obtuse. And if the two rays are perfectly aligned, the angle is straight: 180°.
To measure well, three moves: place the centre of the protractor exactly on the vertex, line up the zero with one side, then read the mark crossed by the other side. Pro tip: before reading, ask yourself whether the angle is acute or obtuse. If the angle clearly looks acute, its measure must be below 90°; this saves you from reading the wrong scale on the protractor!
Angles also add up: if two angles sit side by side around the same vertex, the total angle is the sum of both. And keep this treasure: in any triangle, the three angles always add up to 180°. It is one of the most beautiful rules in geometry.