What it does

Tool	Shortcut	How to use it
Circle	C	Click the center point, then click a point on the circumference (you can type Ø)
Center Arc		Click the center point, the start point and the end point (Arc by Center-Start-End)
3-Pt Arc		Click the start point, the end point and a point on the arc (Arc by 3 Points)

Where to find it

Sketch ribbon › Draw, or right-click › Circle / Arc

Note: Apply Smart Dimension to a circle, then press R or D to switch between radius and diameter.

This keychain bottle opener is made only from arcs, two lines and one circle. Cut it from 3 mm stainless steel and it really opens bottles.

Click Sketch and press Enter (XY-Plane). Choose 3-Pt Arc. Click the start point at about (18, 9), the end point at about (18, −9), then a point on the arc at about (−20, 0), left of the origin. This is the round head, which is more than half a circle (Center Arc only draws the short way round, up to half a circle).
With Line, draw from the top end of the head arc to about (60, 9). Press Esc. Draw a second line from the bottom end to about (60, −9). Auto H/V makes both lines horizontal.
Choose Center Arc again. Click the centre at about (60, 0), then the end of the bottom line, then the end of the top line. This rounds off the tail.
Choose 3-Pt Arc. Click (4, 8), then (4, −8), then a point at about (−12, 0). Close it with a Line from (4, −8) to (4, 8). This straight edge is the lip that grips the cap.
Press C (Circle), click the centre of the tail arc (Center snap), type 5 and press Enter. This is the key-ring hole.
With Smart Dimension, set the head arc to R20, the tail arc to R9, the distance between the two arc centres to 60 and the 3-Pt arc to R10. Add Tangent between the tail arc and each line if they are not tangent yet.
Click Finish Sketch, then Extrude the profile 3 mm.

Challenge: Change the head to R22 and see the lines and the tail follow, because the dimensions and constraints drive the shape.