Hydrogen and oxygen would like to have stable electron configurations but do not as individual atoms. So, oxygen shares one of its outer electrons with each of two hydrogen atoms, and each of the two hydrogen atoms shares it's one and only electron with oxygen. This is called a covalent bond. Each hydrogen atom thinks it has two electrons, and the oxygen atom thinks that it has 8 outer electrons. Meanwhile on the other side of the molecule, the electrons of the oxygen atom give that end of the molecule a weak negative change.
Water is an example of a polar solvent, capable of dissolving most other compounds.
At the temperature range of seawater, the weak hydrogen bonds are constantly being broken and re-formed. This gives water some structure, but allows the molecules to slide over each other easily, making it a liquid. A calorie is the amount of heat it takes to raise the temperature of 1 gram of pure water 1 degree C at sealevel. Therefore, it would take 100 calories to heat water from 0 degrees C, the freezing point of water, to 100 degrees C, the boiling point. C. This is called the heat of vaporization.