There are several factors that affect what kind of work a jigsaw can do.
Wood and light materials – If you're primarily cutting wood, you do not need very high cutting capacity, no more than 90 millimetres. Other features such as speed adjustment allow you to work more accurately in the material while the pendulum stroke function makes cutting more time efficient.
Metal and hard materials – If you're cutting metal or other hard materials, you need a higher cutting capacity, often this is also specified in a separate millimetre measurement for metal. If the saw has a pendulum stroke function, it's important it can be switched off as it should not to be used when sawing metal. In addition, use blades specifically intended for metal. These blades have finer teeth.
Jigsaws come with either mains connection or battery. Battery power gives you more freedom of movement and you don't have to worry about access to power, but the compromise is that they rarely have the same capacity as the mains-connected models when two models are compared on price. They are therefore suitable for people who will use it occasionally, often on soft materials such as wood, and who prioritise flexibility over power and low price.
The time will come when you need to change the saw blade on your jigsaw, either because it's worn out or because you need to cut a different type of material.
Have you never used a jigsaw before perhaps this guide might help you to get started, and in no time you'll be jigsawing like a pro!