Let's go back to building chords. We talked about building triads with intervals of 3rds and now we're going to look at playing the same triads as different intervals. The notes will all be the same, but in different positions. For example:

G                                                                                                       C
E                                                                                                       G
C      is the root position of C major triad. It can also be played as   E . This is what is called the 1st inversion of the same chord, same notes, different positioning of the notes. This same chord can also be played as  E, C, G    - This is called the 2nd inversion of the C major chord.

In  both of these inversions, 1st and 2nd, notice how the different positioning changes the intervals.

C
G
E  = E to G is still an interval of a  3rd, but on the bottom, in the 1st inversion and G to C is an interval of a 4th, on the top.

E
C
G = G to C is the interval of a 4th, but on the bottom in the 2nd inversion, with C to E being an interval of a 3rd, on the top.

For some students it may be easier to think of the triads in terms of scale degrees instead of intervals, so let's take a look at that. If you would like you may refer to an older post about major scales that looks at scales degrees and how they work.
With the scale degrees being 1, 2, 3, 4, 5, 6, 7, 8,  for each scale (C, D, E, F, G, A, B, C) you can look at how the notes line up with the degrees. C=1, D=2, E=3, F=4, G=5. etc. So if you take scale degrees 1, 3, 5, you will have the notes C, E, G which are the C major triad.

Any questions or comments are welcome. Hope this is helpful.