Learning basic math -- addition, subtraction and multiplication -- for adults is no different than learning basic math for children. The only real difference is that an adult's other cognitive abilities, including language, are usually better developed than those of a child at the same stage of math learning. So it's usually easier to explain the concepts to an adult than it is to a child.
Addition and Subtraction
Start getting a grip on the basic concepts of addition and subtraction by using five of an identical item. These could be five oranges, five grapes, five tennis balls, five bricks... five of anything.
Line up all five objects and count them. Now remove one object from the lineup and place it to the side. This is the same as subtracting one from your original number, which was five. What is five minus one? Count the remaining objects to find out: four.
Return the object you removed to the lineup. You had four objects, now you have added one, and as you can see, there are now five objects again. So four plus one equals five -- the evidence is right in front of you.
Reset your lineup of five objects, then repeat the exercise while removing two, three, four and, finally, all five of the objects. Once you've removed an object and calculated the result, add it back in and recalculate the result.
Expand your grasp of the subject, now that you understand the basic principle of it, by memorizing addition and subtraction tables. (See the Resources section for links.)
Use a large number of identical objects, such as grapes or marbles, as your visual aid.
Place one grape on the table in front of you. Now place another grape beside it. You've got one grape, twice -- in other words, one times two. If you count the grapes, you'll see that one times two is a total of two.
Note that since you have two grapes in front of you already, you're perfectly set up to practice two times two. Just put down another set of two grapes next to the first two. You've got two sets of two grapes -- the same as two times two -- and as you can see by counting, the total is four.
Take one grape away so that you've got one group of three grapes. If you multiply that group of grapes by two -- in other words, by representing it on the table twice -- you'll see that you have six grapes.
Reassure yourself that this principle works for other numbers, too. For example, if you set up three groups of four grapes -- three times four -- then count the grapes, you'll see that you have 12 grapes. So three times four is 12. Now you can expand your grasp of multiplication by memorizing multiplication tables. (See the Resources section for a link.)