FCPX optimize and convert media

Hello everyone, I have fcpx 10.4.3 with high sierra and I wanted to know how to do, I always worked with 1920x1080p files and now a friend gave me some files 3840x2160 24p I tried to work with these files but my Mac makes a little effort and also since the final video will be in 1920x1080p q this point I find inuitle edit in 4K but I would like to convert the clips in 1920x1080p so that my Mac works more easily.
now I wonder how to set up the project? so how much the clip 3840x2160p and fcpx converts it to 1920x1080p on the browser?

I tried to set the project as attached, but I find the clip on the browser and also in the timeline always 3840x2160.
thanks to who helps me.

Set the project to 1080, select all video clips in the browser, right-click >transcode to >proxy. Problem solved.

So I open a new project on fcpx in 1920x1080p then amount on the browser the native 3840x2160p clips, and dop I select all and right transcoding / right button right?
then when I select in and out on the clip and put it in the timeline this clip will be in 1920x1080p, I got it right?
thank you

One more thing I did not understand, where do I see if the clip put in the timeline is really in 1920x1080p?
thank you

ps (another system would be to convert 4K clips to fullHD first with edit ready or wrong?)

The browser data will always show the size of the original clip. When you drop those clips into a 1080 project, they will export as 1080. Nothing else you need to do. The transcode to proxy is only for allowing your system to more easily playback the 4K clips if it won't otherwise natively play them back smooth. Be sure to change from proxy to original before you export your project.