This is meant to be a simple explanation to differentiate base from alkali. This is a common question among students.
A base is usually a metal oxide. For example, sodium oxide, potassium oxide, calcium oxide.
If the base can be dissolved in water, we give them another term called alkali. For example, sodium oxide dissolves in water to form sodium hydroxide. Now we can call sodium hydroxide to be an alkali.
In general, any chemical name ending with the word hydroxide can be treated to be an alkali.