A VOR sends out 360 radials.
These are like the spokes of a wheel.
When standing in the center of the VOR looking down a radial, the direction in which you are looking gives the radial its name.
For example.
Looking from the center due South is the 180 radial.
If you move along that radial with the OBS set to 180 the flag will show FROM.
From that it follows that whenever the flag is FROM and you turn the OBS until the needle centers you will be on that given radial.
Flag FROM OBS 270 -> you are on the 270 or due West radial from the VOR you selected.
If you want to fly to the VOR you find the radial you are on. Then turn the OBS onto the reciprocal heading (which is 180 degrees the opposite of the radial you are on) the flag will change to 'TO' and fly towards the heading your OBS indicates.
This is assuming no wind. If there is wind you will need to correct for the wind otherwise you will be blown off the radial you are tracking.