Plants get water from the soil through their roots, along with some other nutrients that they need to grow- but how does the water get from the soil into the roots, and then up to the leaves? Plants suck the water up.
The suction is caused by the evaporation of water from pores in the leaves at the top of the plant, water leaving the plant through these pores pulls more water up through the plants veins. These veins go all the way to the roots of the plant, and the force of the suction pulls water out of the soil.
This is important not just for the thirsty plant, but for everything around us. The water that evaporates from the leaves of plants is what makes up most of the clouds in the sky, and the rain that comes from them. No plants means no rain, means no fresh water.
There is something else interesting about the suction through the plants veins. It means that the sap inside those veins is under negative pressure- if you stuck a straw into that vein you would find that it sucks against you. This is exactly what some sap-feeding insects do, and they have to pump very hard to suck the sap out of the plant, because the plant is sucking back at it.
Mainly through their roots. They grow roots down into the soil which are there to take up water and other nutrients dissolved in the water. Scientists have recently discovered there are also often tiny threads of fungi in the soil which work hard to help the plant roots with this, and in return the plants reward the fungi by offering them sugars as a thank you.
Through their roots. By osmosis, osmosis plays a central role in the movement of water between cells and various compartments within plants. In the absence of transpiration, osmotic forces dominate the movement of water into roots.