Please find below the steps to add the jar file.
Right Click on the project name --> Properties, once you click on properties a pop up windows comes up.
Select Java Built Path from the left hand panel of the windows ---> Select Libraries from the tab present at the top on the right hand side.
After that click on Add external jar -->Browse the location of downloaded jar file.
Add the jar file to your project and then you can check that all the error will be resolved,
Please feel free to revert if you need any further help