How do you get all three fingers on one fret when trying to play an A chord in the second position on the guitar? It is really hard to do.
This is a good opportunity to explain how using a one finger bar chord shape to play the A chord is a better solution than trying to place the tips of three of your fingers on one fret. By simply using your first finger to bar the notes you are going to make this much easier to play. Strumming the fifth (open), fourth, third and second strings give a good robust sound, and you do not even have to play the first string.
As you can see in the diagram, you can simply use one finger to press down on the fourth, third and second strings instead of having to squeeze three of your fingertips onto the single second fret.
Sometimes however you will want to play the A chord with the tips of your first, second and ring fingers all tightly fit onto the second fret because you want to have the open high E string ring out along within the A chord. This would require strumming all strings except for the low E string. This is harder to do physically though so use the bar chord approach as the diagram shows. This will make it much easier for beginners to be able to play the A chord.
The bar chord approach works well with all other chords yet the A is somewhat unique since it only require the use of one finger to play it this way.
Other ways to use this technique with only one finger can be applied using open tunings. Otherwise you will need to use more than just one finger to actually bar most other chords.
You could however do this with a root/fifth E and D chord as well in a variety of chord progressions. Obviously i-iv-v or i-v-iv-v progressions are good examples in this instance. Double stops and power chords also come to mind. This works with root/forth too and putting a lot of double stops into licks and guitar runs can really add some style to your playing. Anyway, try it out, you should find it makes it a much easier way to play the A chord this way.