you can use
Code:
VECTOR vec_name; //then use vec_name.x, vec_name.y and vec_name.z
otherwise use ANGLE ang_name; //then use ang_name.pan, ang_name.tilt and ang_name.roll


for skills you'll see in compat.h
Code:
#define skill1 skill[0]


so for definig your own skills either decide if you're using the array skill[0] or skill1 just for simplicity (even though they're both the same things
Code:
#define HEALTH skill1; //same as #define HEALTH skill[0]

//then later in your project maybe an action?
action act_bobo(){
   my.HEALTH = 100;
   //same as my.skill1 = 100;
   //same as my.skill[0] = 100;


for flags my.VISIBLE
Code:
now you need
set(my, VISIBLE); //which is defined in acknex.h, to set panels visible

//though ENTITIES use reset(my, INVISIBLE);


you can also use toggle as Michael says, which will automatically toggle a flag
Code:
toggle(my, VISIBLE);


and to then check if something is visible use
Code:
if(is(my, VISIBLE)){ //work you magic


in layer models, you'll need to place the .x ahead of the camera
Code:
ENTITY* shotgun_onscreen =
{
  type = "shotgun.mdl";
  layer = 2; // display above view entities with layer 1
  flags2 = SHOW; // lite-C only: visible on screen from the start  x = 100; // place 100 quants ahead of the view
  y = -50; // 50 to the right
  z = 0; // and center vertically
}


hope this helps