To make it follow, simply set the pev_aiment field to a player you want it to follow (or another entity) then set move type to MOVETYPE_FOLLOW.
All the information on how to do this is availabe in turtorials and other plugins. The only thing I see you having trouble with is following, so here's come quick code:
Code:
// 'ent' is your entity, 'id' is the index of the player.
set_pev(ent, pev_aiment, id);
set_pev(ent, pev_movetype, MOVETYPE_FOLLOW);
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