Hi @Kalhori,
So, the problem is you have placeholders in the Apache configuration which should be replaced with actual values, among which @APP_DIR@. These are replaced when running the configuration scripts.
I believe in your case, you are running a single Kaltura server machine, and so, you should run /opt/kaltura/bin/kaltura-config-all.sh and provide the inputs when prompted, the script will then go on to replace the tokens in the config files and things should then work correctly.
If you get any errors while running the config script, please post them here.
Thanks,