Let's begin with the me questions. Me is the object pronoun corresponding to the first person singular (the subject pronoun is yo, of course). It works both as direct and indirect object (just like English me).
No me lo puedo creer.
This is not a typical use of me as object pronoun. Instead the verb creer is used in its so-called pronominal form. There are a lot of optional pronominal verbs in Spanish where you won't find much difference between the two forms, like for example caer and caerse. In this case, No lo puedo creer is also correct.
pensar que me gustas
How to use the verb gustar is a topic in itself. It just works like that. Gustar doesn't mean "to like", it means "to please". Basically what in English you would use as the subject you must place here in the object position and vice versa. There are not many verbs like these in Spanish. Faltar is another (me falta algo = "I am missing something", lit. "to me is lacking something").
me ayudó bastante en el trabajo
There are rules as to where the clitic pronouns go in the sentence. In general they go before the main conjugated verbs, as in this case, and after the infinitives and gerunds. This is another full topic in itself.
You need el before trabajo because that's how things work in Spanish; definite articles are used much more often than in English. Note that in English you say "at work", "at home", "at school", etc., but these are all fixed phrases or idioms. Even in English you'll say "at the office", "at the door", etc. In Spanish these fixed phrases where you can omit the article are just fewer. Also, en el trabajo can both mean "at work" or "with the work [I was doing]".
Dio un consejo al niño.
The most correct traslation of this would be "S/he gave the child a piece of advice." Unlike "advice", in Spanish consejo is a countable noun, so you say un consejo, dos consejos, tres consejos; el consejo, los consejos. For practical purposes, however, you can simply translate consejo as uncountable, unless the example somehow emphasizes that it was only one specific piece of advice.
