Hi Sandra and Welcome to the Tree!!!
If you are unsure what a GEDCOM file is and how it can help you transfer your research to WIkiTree, please take a look at this page I put together to help the first time GEDCOMpare user.
GEDCOM File Usage Primer
It has links to explain a GEDCOM file and many links to WikiTree Help Pages as well. Plus there are some hints and tips on transferring your Tree here.
Vivian is correct that you need to split your total tree into more manageable groupings. As WikiTree does not automatically load the names from your file and create a tree, smaller files make life easier.
Though it can look daunting at first, it is well worth the effort to transfer your research to WikiTree to archive it where it will be available to your family for a very, very long time.