When using a slide rule, you have always to determine the position of the decimal point in the answer by first doing an approximate calculation in your head or on paper. The slide rule gives only the digits in the answer.

Multiply x by y:
Use the moveable cursor to place 1 on scale C above the number x on scale D. If y is off the end of scale D, use 10 on scale C instead of 1. Slide the cursor to number y on scale C. Read the answer from scale D.

Divide x by y:
Use the cursor to place y on scale C above x on scale D. Move the cursor to either 1 or 10 on scale C. Read off the answer from scale D.

Square x:
Move the cursor over x on scale D. Use the cursor to read the result from scale A.

Find sqrt(x):
From you estimated calculation, decide whether the result is going to be in the left- or right-hand half of scale D. Taking care to use the correct choice on scale A (either 7.6 or 76 for example), move the cursor over x on scale A. Use the cursor to reaad the result from scale D.