How To Make Travel Arrangement As Administrative Assistant

As an administrative assistant, I am looking for advice on how to make travel arrangements. I need to know what the best process is and what resources I should use. I understand that I need to book flights, hotels, and rental cars, but what is the best way to go about doing that? Is there a particular website or app that I should use? What other things do I need to consider when making travel arrangements? Any advice would be greatly appreciated.