To order the numbers from least to greatest, you need to first make it so that all the numbers are in the same form
5.006
5.917
5.080
5.990
The ones place all has 5 so we can ignore that.
In the tenths place the largest number is 9, so 5.917 and 5.990 are potentially the greatest
In the hundredths place 9 is the larges number, therefore 5.990 would be the greatest, and 5.917 would be the next greatest.
In the thousandths place 5.917 has the largest number so that would come third, and 5.006 would be the smallest number because it is the only one left.
5.99 > 5.917 > 5.080 > 5.006