Difference between like and as. Diferencia entre "like" y "as".

LIKE
1- The word "like" is a preposition, it means a word that links another words:  

• She walks like a duck. 
• The manager is like a father for Robert. 

2- "Like" can imply a relation between two things that are similar but are not the same thing (comparison). In the last sentence "the manager" actually isn't the father of Robert, but he acts like his father.
3- The complement in the sentences with "like" is simple, is a noun without any verb. "a duck", "a father", etc.  
AS
1- "As" is a conjunction, one word that relates two or more phrases.

•  I as the attendant have to do it..

• The engineer has worked as calculist for three years.

2- "As" involves a description of the subject..It is not a comparison. In the first statement "I" am an attendant. In the second "the engineer" is a calculist.

 

HOW

1- The word "how" is an adverb, a word that complements and explains to verb.

How did she do it? - I don't know how she did it.

Let me show you how do it.