Can someone explain me the constructions (or however they are called) with the "Will + be + verb -ing)" and the "Will + verb" ?
Will + be + verb-ing
This is the future continuous/progressive tense. It describes an action that will be on going or in progress sometime in the future. It is often combined with a time reference. For example:
"Can you go shopping with me this afternoon?" asks one.
"I will be visiting my neighbor this afternoon," responds another.
The response indicates that a visit will be in progress "this afternoon."
The future continuous tense can be used without the time reference, but that presumes a time reference was provided or implied earlier in the discussion or narrative (or the statement doens't make sense).
"What will you be doing at seven o'clock?" asks one.
"I will be visiting my neighbor," responds another.
Will + verb
This is the future tense or simple future tense. It only indicates that something will happen in the future, but tells us nothing about the nature of that event. It is often used with a condition, meaning something must be completed first before moving on to the future task. For example:
I will visit my neighbor when I'm done sewing.
The future task is "visit my neighbor." The condition that must be completed before that task is "sewing."
The future tense can be used without a condition. For example:
"Who will clean up this mess?" asks one.
"I will do it," responds another.
First, it is important to grasp the fact that English does not have a future tense. If anyone tries to tell you otherwise, show them the door immediately.
Instead of a future tense, English uses a number of different ways of indicating future time.
Syntactically, the modal auxiliary verb will has two tenses: present and preterite. Semantically, it is used to make reference to future time (about 80% of its occurrences, I believe) but also for expressing volition (as in I keep telling my son to get his hair cut, but he won't; so I've told him he has to --- notice, the refusals to get his hair cut are in the PAST, and this sentence actually entails that there IS a haircut in his future!).
The film will be seen at the Sundance festival is syntactically a present tense clause with "will" as the tensed verb. But in this example, will clearly expressed reference to future time -- something that could be done in various other ways as well (The film is going to be seen at the Sundance festival, The film is about to be seen at the Sundance festival, etc.).