As you know, green plants absorb light energy from the sun, and also water from the soil, to make their own food.
This process is called photosynthesis (get used to the name, you will hear it a lot in the future!).
Different types of plant have particular adaptations to maximise the amount of light and water they are able to absorb. They are also adapted to other factors of their environment, such as temperature, mineral content of the soil, other plants and animals around them, etc..
Some plants, like the cactus, are adapted to living in hot, dry deserts.
With the lack of water, cacti tend to have deep roots and thick stems that store water. Instead of the thin leaves you're used to seeing on plants, which would lose water, they've developed their leaves into spines.
Some plants, like these bulrushes, are adapted to living in ponds and small waterways.
Water plants have a variety of adaptations to their environment: these bulrushes have roots that hold on to mud and can cope with being constantly submerged.
Over long periods of time, adaptations which are very successful and help individual plants to thrive, become common in almost all plants of that particular species. This is part of the process of evolution for that species.
Some trees have evolved to live in hot, wet places, creating rain forests. Other trees grow in climates which change across the year, from cold winters to hot summers. They have to adapt to these changing environments - or die!
Let's use this information to help us work our way through the questions.