nanpa - number               
tu - two; to divide
wan - one; to unite
weka - away; to remove, to eliminate

The Numbers in toki pona

Cardinal Numbers
In Toki Pona: wan (1) and tu (2). .The word ala can be used to mean 0.

When we need to make higher numbers, we combine these numbers together. Essentially, you just string wan and tu together to add up to the number you want. For example, here's how you add tu and wan together to make 3:   tu wan = 2 + 1 = 3
Neat, huh? Here are some more examples:
   tu tu = 2 + 2 = 4
   tu tu tu wan = 2 + 2 + 2 + 1 = 7
These numbers are added onto nouns just like adjectives:
   jan tu wan = 3 people
   jan lili tu tu = 4 children

But if everybody understand English numbers , why bodering ?

As you can see, expressing higher numbers quickly becomes tedious. Toki Pona was designed this way intentionally to encourage you to focus on simplicity.

The use of  mute.
jan mute li kama. -- Many people came.
jan mute mute mute li kama! -- Many, many, many people are coming!

jan mute lili li kama. -- A small amount (of) people are coming. 

Ordinal Numbers
jan pi nanpa tu tu -- person of number 4; 4th person

ni li jan lili ona pi nanpa tu. -- This is her second child.
meli mi pi nanpa wan li nasa. -- My first girlfriend was crazy.

Other Uses of wan and tu
wan can be used as a verb. It means to unite.
  

mi en meli mi li wan. -- I and my girlfriend united. My girlfriend and I got married.

tu used as a verb means to split or to divide.

o tu e palisa ni. -- Split this stick. Break it into two pieces.

The word luka
The word luka used to mean 5. This use of luka was removed to keep the language's focus on simplicity.

The use of weka.

As a verb, it just means to get rid of, to remove, etc.