When Saturn transits the 12th, 1st and 2nd signs from your moon sign, the roughly seven and a half year period is called Sade Sati. Saturn stays about two and a half years in each sign, so there are three phases.
The three phases
First phase: Saturn in the 12th from the moon sign
Second phase: Saturn over the moon sign
Third phase: Saturn in the 2nd from the moon sign
Common misconceptions
Sade Sati is not always bad. Saturn is seen as the planet that teaches discipline, hard work and responsibility. The effect depends on the whole chart and dasha.
What to do
Keep a regular routine and work honestly
Help someone in need on Saturdays
Rather than worry, have your kundali read by a pandit