Annotate Schematics in Altium

What is annotate? Why should I do it and some tricks.
Probably at this point you already have noticed that all components have this question mark in their designator. Also you have seeing an underlined zigzag red line over all your components, right?
Well, is very likely those both things are caused because you didn't do the annotate yet.
The annotate will automatically nominate the references of your components, considering where they are in the page.

The annotate should be the last thing you'll do in your project and it has several options but let's keep it simple and fast.

Turns out your schematic is done and you'll fix all components references.
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At your schematics file, press t+a+a

Now go to "Update Changes List", then "OK" and finally "Accept Changes (Create ECO)"
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At the new window Execute, make sure is all green and Close.

At this point your schematics is fixed, if you still is seeing the underline red is because the connection has some problem (may not be there).
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OK, but now let's pretend you had a modification and inserted a new component. What to do?

If you redo the same steps it works, but your last component will not be indexed in the same order of the others. To avoid it is always a good practice "Reset all" first. It means you should click "Reset all"->"OK" before clicking in "Update Changes List".
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TIP: Is a good practice drawn your schematics always thinking about how you'll route your board. Sometimes circuits have ICs with internal identical parts as logic gates, operational amplifiers, buffers, drivers, flip-flops, etc.

If you follow this good practice you'll choose the internal part that best matches the pinout for easy routing. If you simply follow the steps above Altium will ignore your choices and reselect the subparts of your components considering only where they are in the sheet, and it's really bad.

To avoid Altium of doing it you should lock the subpart of your components.

At the schematics page press t+a+a

Now right click in the "Proposed Change List" components list and go to "Part ID"->"Lock all Part ID"

Keep following the steps above to update or reset your changes list and you don't need to worry about replacing your subparts anymore.