"I need to put the clothes in the suitcase."
Translation:Eu preciso pôr as roupas na mala.
I believe that the difference is subtle and you would just learn via more exposure to the language. However, there are certain contexts where you would generally undertake to use a specific one over the other. "Eu preciso colocar as roupas" " I need to put on the clothes" Eu preciso por o bolo no forno" Colocar is more abstract I believe. For things you do not literally transfer from a to b. You would use colocar if you wanted to put the pieces together of something (a question, siutation) but por for things that require physically moving around .