I've unmapped cleaned paired end sequence data in fastq format of a bacterial genome. I want to get a sequence data in Genbank format in the end. What are the exact steps that I have to follow in galaxy webserver and if in some point necessary, also using linux based apps? I would appreciate a lot of details.
The steps needed to assemble a genome in Galaxy are layed out in the Assembly training material from the Galaxy Training network. The software for this should be available on the main galaxy servers (e.g., usegalaxy.eu). Since you have a prokaryote, I suggest you follow the "Unicycler Assembly" workflow, which is also available on usegalaxy.eu.
I think the reason for your confusion is vocabulary.
The keywords you search for are genome assembly (see @Devon Ryan's answer) a process that is trying to stick together reads to recreate the sequenced genomic sequence. The assembled sequence needs to be annotated if you are interested where are the genes or what they could possibly do. If you will search for tutorials using these keywords you will find plenty.
I am not sure why you need it, but Genbank format contains the genome (the product of genome assembly), metadata (who is the submitter, what species it is, etc) and genome annotation (what is in the region of genome).