I have an idea for a product that will be used in the construction industry. Can I just put up a web page and immediately start selling it?
This assumes you have the product actually to sell. If you start selling the product without first getting a patent on it, then you are likely to lose the ability to protect it and your competition could muscle in on your invention.
You need to do an FTO (freedom to operate) search before entering the market with your product, or you could be infringing someone else’s patent(s). Infringing another’s patents is likely to have a poor outcome for you as injunctions can shut you down and damages mean that you will be working for them for nothing.
You also need to ensure that you comply with the relevant safety and other regulations within the construction industry before launching your product.