I've created two different instances in AWS EC2 which are used for single purpose (SFTP) . I wanted to group/store these two instances(ex: under one single folder,may be) so that in future I'll get to know these two instances are be used for SFTP purpose.
As datasage mentioned we can use tags. In order to search for resources under a tag, go to "Tag Editor" under AWS. Provide details like Key name that you used while creating a tag and it will display you all the resources that you've tagged.