how to attach excel file in excel community

Kuppanagari_Pavani 

Some users see an area below the box where you compose a post with text "Drag and drop here or browse files to attach".

If you don't see that box, you cannot attach a file here.

As an alternative, you can upload the file to a cloud service such as Google Drive, Dropbox or Onedrive, then obtain a link to the uploaded file and post that link in a post/reply.