The difference between qualquer, alguém, algum and cada doesn't represent any problem from a practical point of view. However if people were asked about the differences, a lot of people would have trouble to describe the differences. That's the same thing in English. English native speakers would never confuse "Someone wants to talk with you" and "Anyone wants to talk with you". It is obvious that the second sentence is wrong or at least it is very difficult to find a context that fits with this sentence, but it is difficult to explain why this sentence sounds strange.
Qualquer (anybody), alguém (somebody), cada um (everybody) are all indefinite pronouns, but they stressses on different aspects. Qualquer means that everbody arbitrarily can be the executor or the goal of an action. Alguém simply refers to someone unknown and everybody is used if everybody is the executorr or goal an action.
Decide in the following sentences which is the correct option. It is possible that various options are possible, choose the one that corresponds to the English sentence.