Using online usability testing platforms is a simple process. Firstly, you will need to sign up for a platform of your choice, such as UserTesting, UserZoom, or TryMyUI. Then, upload your design or enter the URL of your site, or use a plugin or extension to integrate your design tool with the platform. After that, you can define your target audience and select the number of users you want to test with by filtering users by demographics, behaviors, preferences, or other criteria. Additionally, create tasks and questions for your users and provide instructions, tips, or scenarios to guide them. Finally, launch your test and wait for the results. You can watch videos of users completing tasks and answering questions as well as analyze data and get insights such as completion rate, time on task, satisfaction score, or usability issues. Reports can also be generated and findings can be exported or shared with your team or clients.