How do I transition from MS Office 365 to Libre?

I got MS Office 365 with a new computer and need to know how to get off that and onto Libre

Depends, if you ever tried MS-Office on that install.
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When yo never used this, it is usually sufficient to remove the icons from desktop and menu (otherwise see below)
Then install LibreOffice.
(Both programs can also be used/installed at the same time. If you use .odt/.ods with LibreOffice and .docx/xlsx with Microsoft no problems will arise. But check, if you only have a starter for MS intended to lure you in a paid contract…)
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If you have used MS365

PS: I changed you tags: Base is the database component of LibreOffice.

My Migration from MS-Office to LibreOffice