There are different forms of hash, in essence it is made from marijuana to produce something with no plant material and mostly THC and other cannabinoids.
Some involve taking the trichomes of the plant (kief) and pressing it.
Bubble Hash involves soaking buds or trim in ice cold water and filtering it through a mesh with very small holes to allow trichomes to pass through.

Hash can also be made by drying and grinding the plant material, soaking it in high proof alcohol or isopropyl for a few days-weeks, filtering and evaporating off the liquid.

Honey oil is made by filling a pipe with plant material and filling it with butane, what drips out the other end is almost pure thc.