The easiest and most effective way is to google! With the help of a Google query, you will see if your product exists on the market and find your competitors.
If a product doesn’t exist, that can be both good news and bad news. It is possible that there are no potential customers for this product. In this case, you will be its first creator and you need to create a whole strategy for understanding and using it. Another question is whether society is ripe for this product?
If the product already exists and you have many and big competitors, you need to understand whether it is worth investing in it at all? If it turns out that you take a very small percentage of sales, then you may not even be able to pay the costs of its implementation / production.

Today, there are many platforms where you can do this.
One way to test a startup idea with targeted advertising is to create a campaign on advertising platforms such as Facebook, Google AdWords, or Instagram and set it up so that it only appears to a specific audience. For example, you can create a campaign that only appears to people who live in a certain region, or to people with certain interests. This will allow you to assess the interest in your idea and decide on the further development of the project.
Also, understand which platform is right for your business. It often turns out that your audience is “not found” in social networks where you are advertised.

Remember that the best platform for new products is Facebook.
Check out new ideas on Facebook. You can get started quickly with it by creating a landing page where potential customers can sign up and be put on a waitlist before the product has even been created. This is especially true for digital services and courses. Often, through a survey in social networks, you can collect the necessary information for the course – your clients themselves will tell you what interests them and what is relevant to them at the moment. And by the time the course is ready, you will already have a database of interested clients.

Given the ability of Facebook to target posts, you will be able to directly “chat” with the right people. Remember, in order to show ads to the right people who are most interested in your product, you must first analyze the target audience. Then come up with a few ad concepts and upload the photos to Facebook.
In addition to paid advertising, to test your idea, it is enough to make a questionnaire on Facebook and put it in your audience group or ask for advice!

There are several other ways to validate a startup idea, including:

Customer interviews: Speak with potential customers to understand their pain points, needs, and whether they would be interested in your product or service.

Surveys and focus groups: Gather feedback from a larger group of people through surveys or focus groups to validate your idea and identify areas for improvement.

Minimum viable product (MVP): Create a basic version of your product or service to test with potential customers and gather feedback.

A/B testing: Test different versions of your product or marketing materials with small groups of people to see which performs better.

Market research: Research your target market and industry to understand the size and potential growth of the market and identify any existing competitors.

Pivot: If your initial idea doesn’t seem to be gaining traction, be open to pivoting to a new idea that may be more successful.

Ultimately, the goal is to gather as much feedback as possible to validate and improve your idea before committing significant resources to it.