This is a classic (not to say retro) point-and-click game. In the PC version, when you want to look at something, right-click on it; when you want to interact with it (pick it up, talk to it, use it), left-click on it.
In the mobile version, touch the person or thing you're interested in, and two icons will pop up: a hand and a magnifying glass. Choose the magnifying glass to just look and the hand to interact with the item. If it's a person and you want to talk to them, choose the hand.
Click/touch the top of the screen to see the menu, including all the items in your inventory.
How do I interact with inventory items?How do I use the notebook?How do I change the settings?
Unlike normal walkthroughs, in Nice Game Hints you can select just the puzzle you want hints for. Here are listed the puzzles for "General Game Info" in The Blackwell Legacy. The guide you choose only contains information about that puzzle, reducing possible spoilers for other puzzles.