Illustrator allows for the quick alignment of objects using the icons featured in the toolbar above the artboard.
However these toolbars tend to centre multiple objects along a single object, or by treating them as individual objects, possibly ruining the alignment of the other objects that you want to align together.
This makes aligning multiple objects together to the middle of the artboard quite a challenging task in illustrator [for a beginner].
A simple solution to this is to group the objects that you want to align together [by right clicking the selected objects]:
Changing the alignment to the artboard by expanding an icon in the toolbar:
And by using the different set of alignment tools that work with grouped objects..