You need to rename the file you place in there as instructed in the readme that came with download.
So, let's assume you have a cup physics NSCS10 mod and you want the open hood car in the player screen.
unzip the NSCS10_v1.0_Make_a_ui_Choice.rar file and inside the folder, select the make_a_ui_openhood.3do file and extract it to your NSCS10 folder.
Now rename that file you just unzipped to make_a_ui.3do
Now go ingame and check the new player info screen with the hood up.
If you want the driver in there as well, you would select the make_a_ui_nodriver_openhood.3do and extract it to your NSCS10 folder and rename that file to make_a_ui.3do
Whatever car you want to see in the player info screen needs to be renamed to work with the NSCS10 mod.
If you use CUP physics it needs to be renamed make_a_ui.3do
If you use CTS physics, it needs to be renamed make_a_cts_ui.3do
If you use GNS physics it needs to be renamed make_a_gns_ui.3do
If there's no file to start with, you still need to rename one of the files inside the zip to the one of the names above and place it in your NSCS10 folder to see a different car in the player info screen.
Hope that explains it better.
