The easy answer is “Conditional Formatting”, which you can find on the “Home” tab of the main menu. (The default main menu, that is, because menus are highly customizable.)
In general, you’ll want to have a New Rule that uses a formula to determine the cells to format. You can make the formula refer to other cells other than the one you’re trying to format, but keep in mind that you may want to use relative or absolute references, depending on the rules you need. (For example, if the word to be checked for is in a particular column, then you’ll want to reference that in your conditional format formula with a $B1 style reference, so that as you copy the conditional format to the right, it still looks at cells in B:B.)
As @JLeslie has noted, the conditional format formula would be “something like”
=FIND( “NO”, UPPER( A1)) > 0
In this formula, the upper-case contents of A1 are being searched for the string “NO”, and if found and the condition is met (the ‘find’ value is > 0, meaning ‘not false’), then the font, fill, border and pattern selections you choose will be applied to the range of cells you specify.
It’s actually more complicated to explain than it is to do. Play with it, and you’ll get it. (And you’ll make a lot of mistakes along the way and learn a lot more that way, too.)
Keep in mind that these kinds of text conditions can be frustrating, so if it’s possible to add a helper column in the sheet to do the search ahead of time and then look for TRUE or FALSE values in that column, that’s a lot simpler.