So you have a choice here and my answer will be similar to what I provided you for "Synonym analyzer".
Default case - When you don't have a Stemming files available - In that case Simple Analyzer with Stemming will not be be to index Stems for the words in your index. For example words like Walk, Walking, and Walker have a common stem "Walk". So searching for Walk will give you results for the other two. However these needs to be part of the index. In absence of which you won't be able to get these results.
Porter Stemmer Algorithm - Using Porter stemmer algorithm you feed in Stemming file for the targeted language and you are done.
This article will help you understand what is an Analyzer, STemmer, Stop Words and other common terminilogies.