Lava flows burn or bury everything they come across.  They can run over houses, roads, and any other structures.  The speed, and the power of the lavaflow depends on the type of lava.  Aa lavas for example can leave the vent with a speed of about 50km.

The surface the lava flows on will be changed by very quickly emplacing a layer of very new and hot rock onto the pre-existing terrain.  The pre-existing terrain is destroyed by the lava flow.

People rarely get killed directly by lava.  However, lava flows may start fires which are a lot more dangerous for the environment around the volcano.

Information supplied by: http://volcano.und.nodak.edu