https://www.ncbi.nlm.nih.gov/genbank/submit/ will give you most of the information you need. The exact route to follow will depend on the kinds of sequence data you have.
Sara Salah Abdel-Hakeem
You have to register an account with NCBI. Then you will have to generate the BioSample and the BioProject (The order does not matter). It will ask you for some information, very easy to complete. Then you record the information of the sequences and at the end it will ask you to upload the sequences. The sequences may have been previously uploaded to an address provided by ncbi. There are several ways to upload the sequences. There is a section of NCBI, within Sequence Read Archive (SRA) that indicates the place where you should upload the files (FTP upload). In this section it gives you the information of the ncbi site address, your username, password, and the place where you should place your files. I have uploaded sequences from the ubuntu terminal, using the ftp command and the ncbi address, username and password.
During each step, you can save the information and enter and exit the system as many times as you want, since the information will remain saved.
It should be clarified that NCBI indicates that not necessarily the BioSample or the BioProyect must be created before uploading the sequences, so the order does not matter.
At the end, you will have a BioProyect that contains the BioSamples, which in turn contains the sequences (SRA).
Once you complete all of them, in a few days you will be given the access code of the sequences.
https://www.ncbi.nlm.nih.gov/guide/howto/find-published-info-gene-sequence/ can help you.