The three bond types
Plain line — bond lies in the plane of the paper. Solid wedge (triangle) — narrow end at the atom on the page, wide end at the atom popping out toward you. Hashed/dashed wedge — parallel bars getting wider away from you, meaning the atom is behind the page. The width direction always points from the page atom to the off-plane atom.
When to use them
Use stereo bonds at any stereocenter — a carbon with four different groups. For chiral drugs, sugars, amino acids, and most natural products, two of the four bonds drawn at a stereocenter should be wedge/dash and the other two should be in the plane. Drawing all four with wedges is ambiguous; drawing none on a chiral carbon hides the stereochemistry entirely.
Reading them in practice
When you see (R)-2-bromobutane, the (R) tells you the spatial arrangement: the Cahn–Ingold–Prelog priorities decrease clockwise when the lowest-priority group (here the H, drawn on a hashed wedge into the page) points away from you. Wedges are how that arrangement gets onto paper.
Squiggly bonds
A wavy line on a bond means "stereochemistry unspecified." Useful for racemic mixtures and for centers whose configuration you don't want to commit to yet — common in mechanism drawings before the stereo-determining step.
Draw this on the whiteboard
Open the OChem Board whiteboard — benzene rings, wedge/dash bonds, and a clickable periodic table built in. No account needed.