how would I use Log2 (the 2 is on bottom)

Examples:

$${{log}}_{{\mathtt{2}}}{\left({\mathtt{64}}\right)} = {\mathtt{6}}$$   because 2⁶ = 64

$${{log}}_{{\mathtt{2}}}{\left({\mathtt{10}}\right)} = {\mathtt{3.321\: \!928\: \!094\: \!887\: \!362\: \!6}}$$   because 2^3.321928... = 10

On the scientific calculator on the Home page here, if you hover the cursor over the log key, the lg2 key will appear.  In the Math(Input=Result) window type log(x,2) to get the log to the base 2 of x.