GC stands for garbage collection. You might have to allocate more space to the JVM. You can do this in the run configuration under vm arguments (assuming youbusw intellij, eclipse should be similiar) or define it directly in your run script.
Could you perhaps share the error ur experiencing? As this is not a lot of information work work with
I must warn you though, the step from PI to Apollo can be a little demotivating. Maybe not if youíre already confident in java. But if you arenít, then Apollo probably isnít the best environment to learm new concepts in.
I suggest to maybe start off with Asteria or Ruse (which is a huge improvement over PI as the old standard). If u insist on trying out apollo, I can set it up for you. Just pm me ur skype