A person or animal is an adult when they have fully grown up and matured. Before you are an adult, you are a juvenile.
Basalt is a common rock made by lava cooling down quickly. Basalt is usually dark grey or black. Depending on how it cools down, basalt can be found in columns like in the picture, in a grid or hexagonal pattern, or even full of bubbles.
A bolt is very similar to a screw but a bolt goes right through whatever you are using it to fasten, and out the other side. The thread on the bolt sticks out the other side and you screw on a nut and washer to hold the bolt tight.
A catapult is a device that can fling a projectile, such as a stone, a long way without using explosives. Catapults are large, and are usually moved arond on a cart with wheels. There are various designs of catapult, powered by tensioned rope, sinew or gravity, in the case of the trebuchet. Catapults were used during sieges to break down the defensive walls of castles or used to throw things into castles. The catapult in the picture is a "turn bucket" style, using gravity and a counterweight to fling a projectile.
A colt is a young male horse, generally one under four years old. The colt in the picture is one year old.
Something is difficult if it is complicated and takes some skill to achieve. The picture is of a difficult puzzle.
Malting is a process applied to grains like wheat but is usually done to barley. Malting involves soaking the grains long enough to make them sprout, and then drying the grains out in a kiln. Sprouted grain is very high in a sugar called maltose. Malted grain is used to make beer and whiskey. Malt is quite often added to milk drinks.
Moulting, also spelt molting, is when a bird or animal loses some of its feathers or fur so that it can grow new ones. Birds and animals usually moult on the change of season, so that they can grow a thick coat for the winter, or shed their winter coat when the weather warms up.
Salt is a mineral that is essential to all animal life, but is toxic to most land plants. Salt is found in the sea, in your blood and sweat and in solid form as rock salt away from the sea. Salt is collected to use for making food either by mining a deposit of rock salt, or by evaporating salty water until only the salt is left behind. The photo is of the surface of a salt lake with piles of salt scraped into mounds, ready to take away.
You do a somersault when you sit or squat on the ground and roll over forwards. Some people can do somersaults in mid air, without touching the ground.