Hello Karthi,
I know you are only few weeks old member. But the question shows that you are very new to SAP also. The query body is different from query title. However, without ignoring any of them I'll try to answer the three parts of the post.
1. Difference between table and tcode:
I suppose you did not mean what it sounds. However if I answer to it, it will be
'A report Tcode is a command to execute a ABAP program which collects information from group of tables and presents to you the way you wanted.'
'A table is a place where the information stored when you create objects like Technical Objects, M/Pts, Notifications, Orders etc..etc..'
2.How to access tables:
Tcodes SE11 and SE16 help you to look into tables, where you can see the structure (means list of fields the table has) and the data inside.
SE11: Enter the Table name in the Table field and hit on Display button. You will see the structure. Click on the Contents button here, you will be taken to Selection screen (just like IW28 etc). Here if you execute with values you will see the contents of the table.
SE16: Here you will skip the structure. You will be directly taken to Selection screen
3.SAP pm Configuration tcodes
There will be long list and every configuration point will not have tcode. I advise, it is not recommended to take route of tcodes for a fresher. He should follow the spro path and while doing that he can verify whether this setting has any tcode or not (Right bottom of the status bar). and if it has try to remember. I am giving one document here which gives you the method of identifying spro tcodes where system does not display in right bottom corner of the status bar. How to find out T-code in different ways in SPRO
Good luck
KJogeswaraRao