[Lidor124]

in the top of your script
new lspdgate;

where createobject located: like here https://sampwiki.blast.hk/wiki/CreateObject
lspdgate = CreateObject(gateid, x, y, z bla bla bla);


whereever u want to place it:

CMD:gate(playerid, params[])
{
if(PlayerInfo[playerid][pMember] == 1) // check if the player is in LSPD faction
{
MoveObject(lspdgate, x, y ,z.... bla bla bla); // like here https://sampwiki.blast.hk/wiki/MoveObject
return 1;
}

that's the basic of opening the gate