A mixture is any combination of two or more substances that can be easily separated by physical methods. In other words, you can undo the mixture and get the separate substances back again. For example, you could take salt and iron filings and mix them together. You could then remove the iron filings with a magnet, leaving the salt behind.
There are two types of mixtures: homogeneous, where every part of the mixture is the same, and heterogeneous, where every part of the mixture is not the same. So for example, pizza is a heterogeneous mixture because you do not get exactly the same thing in every bite. Vanilla ice cream is a homogeneous mixture because it is the same throughout.
A solution is a particular type of homogeneous mixture where one substance is dissolved in another so the result is a single phase. So if you dissolve sugar in water, you get a solution of sugar water.
The term mixture is very broad, covering every possible combination of different substances mixed together. Solution refers only to those mixtures that are homogeneous, and a single phase.