What is SAP PM?

The R/3 Plant Maintenance (PM) application component provides you with a comprehensive software solution for all maintenance activities that are performed within a company. The uniform, graphical user interface is particularly user-friendly and quickly meets with acceptance, thanks to the numerous possibilities that are available for tailoring it to meet individual requirements.

The data and functions of all maintenance procedures performed within a company can be fully interconnected.

The openness of the R/3 System enables you to use external systems that are integrated with the PM component, such as geographical information systems (GIS), computer-aided design (CAD) systems and supervisory control and data
acquisition (SCADA) systems.

Like to know all transparent Table relate with PM module. 

Try SE80 than fill the program related to PM transaction.
View Dictionary structures you'll get all table that related with PM
Trasaction code that used in PM eq. IW31, IW21, IW41

Try tcode DB15 
Fill the object that related to PM Module 
PM_EQUI              Equipment
PM_IBASE            IBase
PM_IFLOT            Functional locations
PM_IMRG             Measurement documents
PM_MPLAN         Maintenance plans
PM_NET               Object links, master data
PM_OBJLIST        Serial Number History
PM_ORDER          Service and maintenance orders
PM_PLAN             Routings
PM_QMEL            Maintenance Notifications

You can get all table that related to PM Object.    

What is the table for FUNTIONAL LOCATION BOM?

Check for the following tables:

TPST Functional Location - BOM Link
STAS BOMs - Item Selection
STKO BOM Header
STPO BOM item
STPU BOM Subitem
STZU Permanent BOM data

Looking for a report which have Reservation No , material, posted quantity along with User ID of person who created the reservation in PM Order?

This is one report I am asked for at every business I work at and there isn't a standard SAP report for what you want. MB25 will give you what you want but the Username on the report is the person who picks the reservation not the person who created it. At one business I was at it reported as "Batch" because the picking run was done in the background.

The report I create is a query using SQVI Quick viewer and then I transport it to SQ01 SAP Query so everyone can see it. The tables you need to use are;

RESB - Reservation, Material number, Requirement date, Required Quantity, Quantity withdrawn, Work order number
RSADD - Date created, User ID of person who created the reservation 
MAKT - Material Description 
AUFK - Work Order description 
AFIH - Revision (as a selection field) 
MBEW - Total valuated stock (SOH)
USER_ADDR - The User ID first name & second name
RKPF - Reservation Header information if required.

Where to get the table which is having user status with Notiifcation number.  (not the system status).

1. From table QMEL get OBJNR(object number) using the QMNUM( notification number).
2. Using this OBJNR get STSMA( Status Profile) from table JSTO.
3. Using the OBJNR get STAT(object status) from table JEST.

   You may/ may not get multiple object status for an Object number.

   System status number will start from E.
   User status number will start from I.

4. To get the text of the status, use the status number (STAT) and STSMA to get the status text from table TJ30T.

We have done this and working fine.