Both 江 jiāng and 河 hé mean 'river':
长江 Cháng Jiāng 'Yangtze River'
黄河 Huáng Hé 'Yellow River'
The sound in 河 comes from 可 kě 'really'.
海 Hǎi means 'sea'.
All three characters have the three drops of water at the side. Remember to draw the third drop of water up from the bottom of the character (not down from the middle).