This is one of the more technical questions, but don't stress if you can't answer confidently. It's worth having a go and understanding some of the possibilities out there.
Supervised Learning
One of the most common ML approaches is Supervised Learning. Supervised means there's a way to supervise the behaviour of your model by comparing its output to a set of correct answers. These answers must be available, and lots of them.
Answers can be categorical (e.g. correct labels for classes such as "Disease" and "Healthy") or numerical. If the answers are categorical, you may wany to use a Classification problem-representation. Classification simply means "tell me the class of this sample".
If the answers are numerical, you can use a Regression problem-representation. Another way to think of regression is as function approximation - the model will learn a magical function to reproduce the correct output numbers given the input features.
Other problem representations
The figure below shows some other common problem-representations.
Optimisation
An optimisation problem involves searching through a space of potential solutions to find candidate solutions that maximize or minimize an objective function. The objective function must be able to provide a numerical score for any candidate solution. All possible solutions must be represented in the space; AI algorithms will try to search the space efficiently to find good solutions. Optimization is typically used when the problem is well defined, but highly constrained and the primary difficulty is finding good candidate solutions. The methods are relatively simple and all outputs are interpretable.
Optimization problem representations include Timetabling and Scheduling, Vehicle Routing, Bin-Packing and other assignment problems. They typically have "hard" constraints (must be safisfied) and "soft constraints" (do your best).
Reinforcement Learning
Reinforcement learning frames the problem as an Agent, which interacts with a World. The Agent receives Observations from the World and must learn to generate Actions which produce high Rewards. A Reward is simply a number which represents the quality of the most recent Agent Action. The Agent interacts with the world over a period of time, usually called an Episode, making many actions and accumulating many Rewards. You must be able to define the reward of any action in any state of the Agent and World, and also enumerate all potential actions, which do not change over time.
Unsupervised Learning
Unsupervised learning is pattern or structure detection in data. It aims to reduce a large amount of data to a smaller set of model parameters which capture it as accurately and comprehensively as possible. For example, clustering of user behaviour - if you can find clusters in your data, you can start to think about what types of user those clusters represent and look for differences in behaviour between those clusters. Unsupervised learning can also be used for dimensionality reduction.
Unsupervised learning usually doesn't directly solve a problem, but it generates insights about the data.