Learn English – the name of the difference between “doesn’t” and “don’t”

In both cases you have a conditional sentence. What if means What will/would happen if... You are right when you say it is used in a question. If on the other hand is used to introduce a conditional clause, not necessarily a question. Here are two examples:

If I told you the truth, what would you do?

You can also have a positive or negative sentence with if of course, as you suggested in your question: If I told you the truth, you'd be hurt. OR If I didn't tell you the truth, I would feel awful.

What if I told you the truth? (This implies the question of what you would do or what would happen.)

The Spanish infinitive marker -Vr is part of the same sound unit as the verb stem it attaches to (it affects the placement of stress), and it can only appear after a verb stem, so it is classified as an affix (in this case a suffix).

English to is normally considered to be its own word (rather than an affix) because it is not all that exclusive about where it can appear w/r/t other words: it can come before a noun phrase, it can come at the end of a sentence, or it can come before a verb in its base form:

...to Rome.
...the door she went to.
...to walk.

English verbs have a base form which shows up after modal auxiliaries, and after to in forming the infinitive:

...will walk; ...can walk; etc.
...to walk.

Spanish has no special verb form corresponding the English base form, but the Spanish infinitive is a pretty close fit.

Note also that the English infinitive has more than one function. Just to name a couple:

• The infinitive is required as a complement after certain verbs: e.g., ...hope to walk.
• The infinitive may have purposive meaning: e.g., ...(in order) to walk.
• The infinitive may be used to refer to a verb phrase in the abstract: e.g., to suffer The Slings and Arrows of outrageous Fortune, Or to take Arms against a Sea of troubles

These functions tend to be translated by the Spanish infinitive, but there are some uses of the Spanish infinitive that are better translated with the English present participle (-ing form). But the English present participle itself is sometimes best translated with the Spanish infinitive, sometimes the Spanish present participle (-Vndo form), and sometimes with the Spanish simple present...