You don't have to use OneDrive's cloud storage. Maybe you prefer a cloud service from another provider, or perhaps you're philosophically opposed to storing files in the cloud. Regardless of the reason, if you don't want to use OneDrive, you are free to ignore it.
When the sync client pops up asking you to sign in, just click Cancel. You can then change the OneDrive settings so that it doesn't run automatically at startup.
That option does, however, leave the OneDrive icon in the navigation pane of File Explorer. To make it disappear, you need to make a simple registry edit.
In Windows 10 Pro or Enterprise, you can use Group Policy to make this change. Open Local Group Policy Editor (Gpedit.msc) and go to Computer Configuration > Administrative Templates > Windows Components > OneDrive. Double-click the policy Prevent The Usage Of OneDrive For File Storage and set it to Enabled.
On devices running Windows 10 Home, where Group Policy isn't available, you have to edit the registry manually. Using Registry Editor, navigate to HKLM\Software\Policies\Microsoft\Windows\OneDrive. (If that key doesn't exist, you need to create it). Add a new DWORD value, DisableFileSyncNGSC, and set it to 1. Restart the PC to make the policy setting effective.
Note that this change applies to every user of the selected device. If you previously synced files to OneDrive, they remain in the local OneDrive folder but are no longer linked to their cloud counterparts.