This is a sample code to create lookup runtime in axapta form
public void lookup()
{
SysTableLookup tableLookup;
QueryBuildDataSource qbds, qbds1;
QueryBuildLink QueryBuildLink1;
Query q = new Query();
;
tableLookup = SysTableLookup::newParameters(tableNum(_Taluka),this);
qbds = q.addDataSource(tablenum(_Taluka));
qbds.addRange(fieldnum(_Taluka, _DistrictCd)).value(District.valueStr());
tableLookup.parmQuery(q);
tableLookup.addLookupfield(fieldNum(_Taluka,_TalukaCd));
tableLookup.addLookupfield(fieldNum(_Taluka, _TalukaName));
tableLookup.performFormLookup();
}