Same code just with comments for each step to explain.

// link CI to Asset just like Assets are linked to CIs

var gr = new GlideRecord('alm_asset'); //create glide record on table

gr.query(); //query all records in table


while(gr.next()) {

     var Id = gr.ci; //get sys_id for CI in alm_asset table

     var cmd = new GlideRecord('cmdb_ci'); //create glide record on table


     cmd.addQuery('sys_id',Id); //where sys_id from cmdb_ci == sys_id from ci on Asset table (Id)

     cmd.query(); // run query


     if(cmd.next()) {

           cmd.asset = gr.sys_id; //update asset field on cmdb_ci table with 

           cmd.setWorkflow(false); //disable running of business rules that might normally be triggered by subsequent actions

           cmd.update(); //commit update

     }

}