Web browsers use a collection of CA (Certificate Authority) root and intermediate certificates in the process of validating the certificates sent by web servers. The root certificates are sometimes called "trust anchors" and the collection is sometimes referred to as the "trust store". These certificates are published by trusted commercial and government CAs.
Some browsers, such as Firefox, use their own trust store. Others use a trust store maintained by the operating system.
When the browser is used to connect to a server that has a certificate issued by a well-known public CA, it must already have the necessary trust anchors and no further work by the user should be necessary. This is usually the case for public web servers.
Servers within an organization might use certificates issued by an organization CA, or generated using a test CA such as the optional Demo CA included with Enterprise Server. It might be necessary to install additional root and/or intermediate certificates into the trust store for the browser to let the browser connect to such a server.
The process for importing trusted certificates varies among browsers and browser versions. For browsers which use an OS-managed trust store, such as Microsoft Edge and some versions of Chrome on Windows, the certificates can be imported using OS tools. See your OS documentation for more information. For other browsers, typically there will be a certificate-import function available in the browser settings dialog, often under a Security tab or similar.
You might need to convert a certificate to a different format, since there are numerous certificate file formats and not all tools support all formats. The openssl utility program included with Enterprise Server can be used for this purpose. Other tools for converting certificate formats can be found online or bundled with the operating system.