I think that soundcheck means that one is testing how good the sound is, right?

EG. We didn't want to watch their gig, we went to drink a bottle of wine behind the loudspeakers instead, but it was good to see them doing the soundcheck.

Yes - they ensure all the microphones and speakers are working, etc.
Thank you for the fast reply GG Emotion: smile
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OK, one more question about a soundcheck.

If someone says: We had to make sure that we had a soundcheck, lights and a dressing room ......

--- does it mean that they had to make someone check the sound and the lights for them or they had to do it themselves???

I have no idea. It sounds like that's what they considered essential to put on a concert.

Lights, good sound, and a dressing room. I think a lot of bands starting out can get by without a dressing room.
OK, once again thank you for your help!!!
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A soundcheck is something that the band and the sound technician do together.  The band is on stage, testing out the microphones and amplifiers, while the sound technician adjusting and controlling the volume of each device.  If a band says "we had to make sure that we had a sound check," that means 
a) that they had to make sure they had time for a sound check, and also

b) that they had to make sure there was a sound technician there.
Thank you for your explanations!