When you obtain a dedicated server or even some VPS setups they may also provide you with dedicated IP's as part of that server package.  Most of the time PTR records do not apply to shared hosting but it really depends on how the host sets up the shared hosting plans. If they also come with dedicated IP's then yes you can also apply for a PTR record to be set up for you. 

We wont go into great specifics of PTR records as there is a link below if you would like to know more.  However the idea behind PTR records is that it your IP will be assigned to your domain name. This allows services and features that you may use to locate your site via reverse IP.

For example your localhost which is always 127.0.0.1 should point to localhost.yourdomain.com and if it does not then you will need to establish a PRT record. 

So how do you check to see if you have PRT records or not, well there are a few ways to do this. First you can check this website  

intodns.com

enter your site name such as example.com and it will show you what is found regarding your DNS records.  In the MX section the last entry there will show if you have a PTR record or not. 

OR

You can look up via linux (bash) command prompt.  For example: 

enter this command > host 127.0.0.1

if it comes back as 

1.0.0.127.in-addr.arpa domain name pointer localhost.

then you are just fine

but if it comes back as 

Host 1.0.0.127.in-addr.arpa. not found: 3(NXDOMAIN)

then you will need to set up a PRT record

notice in both cases that the ip is in reverse, this is why they call them reverse looks.  Also notice that the result has a .(dot) at the end of it.  That dot is VERY important and if you want to read about that .(dot)  you can do so on just about any DNS wiki page.  That .(dot) is really what controlls your DNS.

Below is the link to the PTR record wiki page if you want to know more. 

https://en.wikipedia.org/wiki/Reverse_DNS_lookup

lets say that you wanted to look up your hostname.  If you dont know what your hosting is, its the name BEFORE your domain, for example hostname.example.com  now there are two hostnames one is created and assigned by you such as the example below, the hostname is titan. The other hostname is assigned by the server when you get your server and they install the OS and that is called the localhost so that format would be localhost.example.com

You want both of those reverse lookups to point at your site.  Well to be clear you want localhost.example.com to be assigned to 127.0.0.1 and you want your chosen hostname.example.com to point to your primary server IP.  

So to check these you can do this at the command line prompt: 

in this example we are checking to see if titan which is the chosen hostname has a PRT record.

[root@titan etc]# hostname  

titan.example.com

[root@titan etc]# host titan.example.com

titan.example.com has address xxx.xxx.xxx.130

[root@titan etc]# host xxx.xxx.xxx.130

Host 130.xxx.xxx.xxx.in-addr.arpa. not found: 3(NXDOMAIN)

so in this case we can see that the alphabetic hostname titan.example.com resolves to the ip (again notice that the IP result is in reverse) even though 130 is actually the lastt 3 numbers of this IP.  

Then we check to see if the reverse ip resolves to the alpha name, and it does not because we do not have a PTR record yet. 

Now how do you get a PTR record?  Well you cant do it yourself unless you own your IP address which means that unless you litterally purchased your ip addresses from and IP seller then you cant do it yourself. 

What you will need to do is start a ticket with your server company or host (whoever assigned the IPto you when you got your package).  And they should have a process by which they can assign the PTR record. Because even though you are using the IP address, they actually own it.

Typically what will happen is that they will ask you to submit all the IP's you want PTR records for in a certain format to them in your ticket and they will assign them for you.  Now understand that this decisions is strictly up to them and their policy.  Some companies refuse to set up PTR records for their clients unless they are on a certain package or unless they pay for the server way in advance(long term customer) or other circumstances. 

Typically format they want is like this (remember the .(dot) at the end)

lets say you need to assign PTR records for 
localhost  127.0.0.1

hostname titan.example.com with ip 123.456.789.556

and one website with ip 123.456.789.555 
typically your submission to your IP owner looks like this:  dot at the end remember!

1.0.0.127.in-addr.arpa. IN PTR localhost.example.com.

556.789.456.123.in-addr.arpa. IN PTR titan.example.com.

555.789.456.123.in-addr.arpa. IN PTR example.com.

once the IP owner submits the request on their end it usually takes up to 24 hours for it to propagate.

i hope this helps someone :)