Enable registration protection
You'll find all settings for No-Bot Registration in your WordPress dashboard in the Tools menu.
People can be a nuisance on your website through various routes. The most common ones are through account registration or spam comments.
Looking at the Registration protection panel in your dashboard you'll find 3 check boxes to protect against spam through those routes. Simply enabling the 'Protect user registration' and 'Protect blog comments' checkboxes should reduce or remove spam by a lot.
This will add a basic security question to the login form and comment form.
If you have WooCommerce installed you may want to also enable the 'Protect WooCommerce checkout pages' checkbox. This adds the security question on the account creation portion of the checkout page, too.
Failure Message
Of-course people need to know why they're not real humans. So enter a descriptive message here informing them of their mistake.
Security Questions
Configure one or more security questions. No-Bot Registration will pick a random question when the page loads. More questions offers more variety. So bots can not easily guess the answer.
If the question always asks is 1 + 2 = 3 the eventually bots will catch on and just guess 3. If you have several questions alternating this becomes a lot harder to predict for bots.
Each question can have multiple answers. For example if your question is to answer what color the sky is. Several answers might be acceptable, such as "blue" or "grey".
Likewise if you ask to solve a simple sum. Say 1 + 2, acceptable answers could be "3", "Three" or "three".
Keep your questions simple and try to avoid ambiguous answers. Asking what color a car or a fridge is, is not a good question as those things come in hundreds of colors and the answer is too much open for interpretations.