Once you've installed CRM for JIRA Cloud, the custom field "Company" is created automatically.
You can find it in JIRA administration/Issues/Custom fields and add it to the screens you need. You can leave it as is with no screens added if you don't need "Company" field in issues.
Now you can select a company name from dropdown list of all companies that are in Companies Directory
You can search by first letters of company name. If you have too many companies in Companies Directory just start to type inn:
You can search by Company field using JQL 'Company = Teamlead' where 'Teamlead' is the company name. Or use a basic mode for issues search:
If the reporter as Jira-user is linked to CRM contact which is linked to a company, the Company custom field will be filled in automatically with Reporter's Company. Autocomplete works only on issue creation and reporter changing, all other issue changes do not affect field autocomplete.