First, I need to remind you about something with decimals:

Remember place values?

9.3284   the 3 is in the 10ths place, the 2 is in the 100ths place, the 8 is in the 1000ths place and the 4 is in the 10,000ths place

So...

.7 = 7 / 10   and   .23 = 23 / 100 (<-this is the one we need)   and  .389 = 389 / 1000

At first, we'll do this in two steps:

1
Use the word "percent" to convert the percent to a fraction.
2
Use decimal place values to convert the fraction to a decimal.

Let's go!

Convert 42% to a decimal:

Step 1: 42% = 42 / 100
Don't simplify the fraction!
Step 2: 42 / 100 = .42

So,  42% = .42