lucene and plurals

If you look at the comment here you'll see

Lucene is very much the tool to do this. If you want apple and apples (plural) to match, you just need to be careful about using the correct language stemmer when indexing and querying the index.

I'm new to lucene and barely understand how adding and saving document work.

How do I search my tag field so apples and apple are the same?

I am using lucene.net 2.9.1

I suppose you're looking for the stemming algorithm here is an example reduced for plurals

You may find how-to-enable-stemming-when-searching-using-lucene-net helpful for .net