Hi Durga,
for worklfow triggering you can make use of event 'TRIGGERED' of class 'CL_HRASR00_WF_PROCESS_OBJECT' and regarding importing values from form to workflow you can use method 'DATAMAPPING' of class 'CL_HRASR00_WF_COMPONENTS'. here you need to pass below in workflow to task binding:
form scenario, form scenario version , workitem id, mapping direction(E->Export or I->Import, here it will be 'I') , Activity(R-read or W-write, here it will be R). Also you need to pass name of field you want to take from form to &FIELD_NAME1& &FIELD_NAME2& &FIELD_NAME3& . please not name of field name of context field binded to your from field.
task to workflow binding
you will get value from form in &FIELD_VALUE1& &FIELD_VALUE2& &FIELD_VALUE3& respectively, bind them to your workflow container. Now you have all the value and you want to sent the workflow to approval, for that make use of WI_EXECUTION_VIA_R3_INBOX method of class CL_HRASR00_WF_COMPONENTS with program exi as CL_HRASR00_POBJ_WF_EXIT.
i think above detail will help you.
Regards
Ajit Choudhary