Absolute beginner needs help

Hi all
Not sure if this is doable but I trying to pull data from an ERP system and using SQL that comes with the app, I have listed the fields below that I require from each table but if I try to use JOIN or any other queries I can’t pull them together, although I can if I do them individually.

Any help greatly appreciated, please remember I am new to SQL queries.

Example
Select MRPPLAN_ITEMID, MRPPLAN_FUTUREDEMAND, MRPPLAN_JOBSTART, MRPPLAN_JOBFINISH, MRPPLAN_MANUFACTURER, MRPPLAN_JOBTYPE
from MRPPLAN (table1)

table1
PONUM, REF, QTY, REQDATE
from PODETL (table2)

MRPPLAN_ITEMID, MRPPLAN_FUTUREDEMAND, MRPPLAN_JOBSTART, MRPPLAN_MANUFACTURE
from JOBDTL (table3)

Would be useful if you can post the query with the joins that did not work, along with any error messages that you received.