Originally Posted by: Itsmesilly
a song I am learning goes from a G to then a D/F#
what is the slash again?
[/QUOTE]
Otter_Lynn gave you the right answer. Good job!
[QUOTE=otter_lynn]
It means that it's a D-chord, but with the lowest note in the chord is now a F#.

Works the same for all slash chords: first note names the chord, the second note names the lowest note in the voicing.

Options for G to D/F#:

E |--3--2--|--3--2--|---------|
B |--3--3--|--3--3--|--8---7--|
G |--0--2--|--4--2--|--7---7--|
D |--0--0--|--5--4--|--9---7--|
A |--2-----|--------|--10--9--|
E |--3--2--|--------|---------|

See my tutorials on chord triads, inversions and voicings for a complete understanding and practice with these concepts.

http://www.guitartricks.com/tutorial.php?input=148
http://www.guitartricks.com/tutorial.php?input=730
http://www.guitartricks.com/tutorial.php?input=731
http://www.guitartricks.com/tutorial.php?input=733
http://www.guitartricks.com/tutorial.php?input=734