as an adjective, simple describes something that is easy to understand or explain, not complicate.
when simple is used as an adjective, it usually precedes a noun; for example, 'a simple explanation,' or 'a simple problem.'
1. This simple recipe takes only three ingredients.
2. She has a simple solution to the problem.
when using simple as an adverb, it's important to remember that it usually follows a verb, rather than preceding it; for example, not 'simply she explained,' but 'she simply explained.' Additionally, simple is often misused in place of 'easy'; for example, instead of saying 'a simple math problem,' it's more accurate to say 'an easy math problem.'