how can ı use iPhoto on my new macbook pro

Also see the Photos user guide: Photos User Guide for Mac - Apple Support

If you have several iPhoto Libraries needing migration to Photos, and the libraries are on external drives, be sure to move them to supported volumes. Photos for Mac is more particular about the file system format of external volumes than iPhoto has been.keep the photo libraries on volumes that have a wired connection and have the file system format MacOS Extended (Journaled) or APFS. Move your Photos library to save space on your Mac - Apple Support

Have you opened Photos application yet? Based on this information, when you open Photos for the first time, it will upgrade your iPhoto library to a Photos library.

https://support.apple.com/guide/mac-help/switch-to-photos-from-iphoto-mchle1529919/mac

Do you mean how can you get your images in the old iPhoto library into Photos?

Simple:

Hold down the option (or alt) key and launch Photos. From the resulting menu select 'Choose Library' and point at your iPhoto Library. It will do the rest.