Press the Windows key (or click Start).
Type explorer.exe into the search box.
Does 'explorer' appear in the results area above it?
If so, does double-clicking that entry open File Explorer?
If it does, repeat the search and then right-click the entry in the results panel in order to select 'Pin to Taskbar'
If that doesn't work, can you open File Explorer via any of the methods suggested here?
http://www.digitalcitizen.life/9-ways-open-file-explorer-windows-10
(If so, which ones?)