In 6/8 time, each measure contains six eighth notes. We are often told that therefore there are six beats in 6/8 time.
But when my band plays a piece in 6/8, the conductor counts in two. Also, the tempo is often denoted with a dotted quarter note next to it; and I once read an SE post (I don't remember where) claiming that 6/8 time does not mean six eighth notes, but rather two dotted quarters.
So are there really only two beats, or are there six?
There are two basic types of meter: simple meter, which divides beats naturally into two parts, and compound meter, which divides beats naturally into three parts.
Time signatures where the top number is a multiple of three, like 6/8, 9/8, 12/8, etc. are usually compound meter. The bottom number in a compound signature indicates the division of the beat.
If you write measures of 2/4 using all eighth note triplets you'll get the same rhythm as if you wrote measures of 6/8 using all eighth notes. Using a compound meter eliminates the need to write "3" over all the beams.
As far as conducting and counting goes, if it's fast it's done in two, and if it's slow it can be done in six.
There are two beats of dotted crotchets in 6/8 time, 6/8 is compound duple time with dotted crotchet beats.
The standard answer is 'two'. Most of the time when you see 6/8, the conductor will beat two in the bar.
4/4 has 4 beats. But sometimes, in a slow piece, the conductor may decide to beat it 'in 8'. In the same way, a slow 6/8 may be taken 'in 6'. But that basic 2 count will still be there.
Don't get sidetracked by 'America'. It shifts between 6/8 and 3/4. Modern music does this sort of thing a lot. A piece notated in 6/8 may constantly shift between 3+3 groupings and 2+2+2 groupings, beween 6/8 and 3/4. We don't always bother to keep changing key signatures.
'America' is often notated as 6/8 in a song copy. In the original score it was given as 6/8(3/4). (And no, none of us have encountered "Seis" anywhere else either! If you're interested, start at paragraph 32 of this: http://www.echo.ucla.edu/Volume2-Issue1/wells/wells.pdf)
According to Dolmetsch, each measure contains a number of main beats—such as the three in 3/4, or the two in 6/8—which are each divided into inner beats. So a main beat in 3/4 time would contain two inner beats (assuming an eighth-note rhythm), while a main beat in 6/8 time would contain three, the eighth notes.
When a 6/8 piece is conducted in two, it's because the piece is very fast, and counting the eighths individually would be infeasible; beats 1 and 4 are the strongest, so it's usually reduced to those two.
However, some 6/8 sections can be counted in three, if your composer or conductor specifies it. 6/8 can even be counted in six, if the piece is really slow.
So whether 6/8 time contains two or six beats is a matter of context.
It all depends on the tempo. If it's fairly slow then it's natural to count six beats in a measure. If the tempo is faster then two beats is much easier. If the tempo is really fast a conductor might only give one beat per bar, and if it's really slow a conductor might even subdivide the eights and conduct in twelve.
If the 6/8 measure is mixed with other time signatures it sometimes makes more sense for the conductor to give three beats. I've even seen "America" from "West Side Story" which has alternating 6/8 and 3/4 bars, conducted all the way through in three. (Not that I think that's a good idea)
6/8 time is 2 dotted crotchets in a bar. The confusion where there are 6 beats, is because there are six pulses; which are the quavers.
