We need to store some additional information about users. For example "name of institution" for teachers. How we can do this in Dspace? Thank you.
This requires some customization.
With "users", you really mean authenticated users that have accounts in the system, or people that are mentioned in the metadata of items in your repository?
First case: Storing more information in accounts (EPeople)
Pre-DSpace 5, this was not an easy challenge. Thanks to the "Metadata for all" work, EPerson data is now also stored as metadata in its own eperson schema.
Just like adding metadata for items, adding a new field for an eperson is now just as easy as adding a field to the eperson schema. You can also add it here if you want to include it during DSpace installation:
https://github.com/DSpace/DSpace/blob/master/dspace/config/registries/eperson-types.xml
Second case: storing more metadata for authors on items
If this is your goal, I would strongly suggest to look at the Authority control work that was done to store author information imported from ORCID. https://wiki.duraspace.org/display/DSDOC5x/ORCID+Integration
The approach would be to store additional information in the SOLR authority control index, and not to jam it as subfields in your metadata.