Sidereal: The time for the earth to go once around the sun, relative to the stars. That is 365 days, 6 hr., 9 min., 9.54 sec.
Tropical, or year of the seasons: The time for the earth to travel from the vernal equinox, once around, and back to the vernal equinox. That is 365 days, 5 hrs., 48 min., 45.92 sec. The lengths of these two years are not the same because precession of the earth's axis causes the equinoxes to move with respect to the stars. How much? Once around in 26,000 years. That's the same as
1/26000 = 3.8×10-5 (times around in one year)
= 3.8×10-5×(24)×(365) = 0.34 hours in one year.
That is about 20 minutes, the difference between the two 'years'.
Which year do we run our lives by? The tropical year - because the equinox determines the season of the year; and we rely more on the seasons than on the position of the stars. Notice that the length of the tropical year is not an integral number of mean solar days. (Integral means 1 or 2 or 3 or 4, etc.) This fact complicates the process of making calendars.