My simplest algorithm is: Take the binary number (e.g. 1011) and write down the place value underneath each number.
1 1 0 1 1
16s 8s 4s 2s 1s
Then add up all the place values that have a 1 in them.
16 + 8 + 2 + 1 = 27
11011 (base 2) = 27 (base 10)
This page gives a more detailed tutorial: http://www.electronics-tutorials.ws/binary/bin_2.html
Note that there's quite a bit more information in that tutorial than what you need to know for our class. (e.g. it does conversions both ways).