Asking them.

Ideally, talking to them in real life. Over the phone/Skype is 2nd best. Surveys are 3rd best (although surveys can be used for other purposes like quantifying simple things over a large sample, which would take too much time IRL).

Prepare a set of 3-5 questions to ask your early customers and get in front of them. It has been insane the amount of stuff I have learned from talking to people using our platform.

In fact, talk to your customers before they even use your product. Show them a page or a piece of copy and ask if they understood what it is you do. I can assure you, if you are in early stage, you will get crazy insights from this type of discussions.

As far as storage, I usually write notes during the meeting (ideally you need two people in the meeting, the 'asker' and the 'note taker', makes things easier). Then, just take a couple of hours rounding up your notes once you are done with everyone. Get 2-3 other people on your team to read it all as well. Have a team meeting and discuss everything together, in real life.

If you do surveys, pretty graphs do it. I am just not a big fan of turning 'human data' (sentences, sentiment, etc.) into 'storable data' (graphs, charts, etc.). It is a lot more valuable than that. Process it as humans and make team decisions.

I send a personal email with a Typeform.com form.

Email them . Offer some type of reward ( we did a product giveaway). Build landing page (can be a Google form also) . Ask just a few open ended questions and the rest multiple choices.

The above mentioned ways by Shahzeb & Ruchi are used for initial promotion of the product.
After this you can brand it through Social Media and increase your reach towards your niche.

And even if you have scripted questions, make sure at least 1 is open-ended.

In the very initial launch of a new product, calling users. All of them to understand their issues/feedback or expectation.
As number of users grow, having a live chat support option and telling them that they can always chat with us.

Take a look at the "golden" questions from this webinar by @sean from a a couple years ago: https://growthhackers.com/articles/golden-questions-that-reveal-exactly-why-your-visitors-arent-converting-slides-and-video-conversion-rate-experts/
Based on your situation, the questions make work as is or with slight modifications