Hello Heba, you have a lot to cover! Sequencing is at the core of other related fields. I would advise you by start reading a good review like https://www.nature.com/articles/nrg.2016.49 . You can also find really easy videos explaining sequencing methods in youtube.
Metagenomic and microbiome are no longer the same thing, some authors are using metagenomic to refer to whole genome metagenomics approach, while labeling microbiome amplicon analysis as metaprofiling. Whichever you wanna learn sequencing is at the core, difference is that microbiome metaprofiling has a previous PCR amplification step. In case you go for this field i advise you to read publications of a specific area (yours first!), because human gut microbiome papers are way different than food related ones.
Hi Heba, depending on your exact field of research, this recently published book might help you in getting started and obtaining an overview of the most important aspects of microbiome analysis:
The answer to your question would be so extensive. It would be the best way to learn some basics of microbiome/ metagenomics/ and sequencing and after this come with more specific questions.
Hi Heba! I have come across an amazing resource at coursera, a course by Rob Knight's group. Totally worth watching, particularly lessons 8 and 9 on week 3.