How do sciatists/astromaners measure distances to stars and stuff?

This has been bigung me for a a year now. You need a device to measure distances (like a tape) or a laser. But stars are so far away that it dut'nt work. My teacher tolded me sciatists and astromaners use geometry to measure distances to stars and galaxies. But that dut'nt make sense. You need a triangle to do geometry. So I'm not buying that **** that they use goemetry to measure distance. Too hard to understand!!!