Why we should use Google Analytics?
Before setting up a Google analytics account it is important to know that why you are are using Google Analytics. There are few objectives for which you create an analytics account

Email Signup
Sell a Service or product
Ads affiliate
Call your business

Why We create goals in Google Analytics?
We create goals just to measure the campaign performance in terms of conversions or sales.

Before creating a goal first decide for what you want to create goal. Is it a Thankyou page after successful sale or a Contactus page or just create event for tracking number of downloads of a video.
How to set goals conversions in Google Analytics?

1. Sign in to Google Analytics account.
2. Select the website profile for which you want to create goals
3. Go to Admin section
4. Click "Goals"
5. Create "New Goal"

Please refer the below image for getting the above process

Image Source: Google Analytics account

6. Here you will see two fields Name & Type. First assign a name for your goal like "thankyou"
7. Now Select a type of goal whatever you want to track from given options (Destination, duration, Pages/screens per session, Event and Smart goal)

Please refer below image for above process.

Image Source: Google Analytics account

There are 5 type of goals you can see in above image. And i will explain all 5 goals in details.

1. Destinations: 
It is the most common type of goal that mostly people use to track the conversion. In this section you will see 3 fields Destination, Value and Funnel. 

A) Destination: 
In destination field you can put the destination URL (/p/thankyou.html). You can put the url just after / as Google already knows your top level domain. There are three options to set your destination URL 

a) Equals to: 
If you have a simple static html URL like "ThankYou.html" page you can select "Equals to". For this process please refer below image

Image Source: Google Analytics account

b) Begins With:
If your destination URL is dynamic you can use "begins with" for example your contact page are generated in many ways like "/thankyou.html?id=4251" or "/thankyou.html?id=3761" or in any other ways. You just have to put the url only "/thankyou.html".
Please refer below image to understand above process

Image Source: Google Analytics account

c) Regular Expression: 
If your website generating more than one thank you pages from different funnel, you can use regular expression. For example if your website containing 2 thank you page "thankyou.html" and "thankyou1.html" you can put both thankyou pages in regular expression. Please refer below image for this process

Image Source: Google Analytics account

Remember Don't use space between two regular expressions

B) Value: 
In this section you may define a value for your goal. It depends on your business that what is the correct value of your goal. For example if you are selling an e book  and that one order cost is $100, then you can set a value of $100.

C) Funnel: 
Funnel is basically path of your destination URL where you expect traffic to take towards the destination. You can use funnels to track user's entrance and exit points.

2. Duration: 
You may select duration if you want to track customers who spend time more than your expectation on your website or those customers who seem very interested towards your website services. For example if you want to track only those customers who spend more than 4  minutes on your website. You can fill values accordingly. Please refer below image for this process

Image Source: Google Analytics account

3. Pages/Screens per session: 
In this section you can setup goals for those customers who visited your website page more than one. For example i want to track only those users who visited my website's 3 different pages. Enter the value 3 with "greater than" option.

4. Events: 
Event tracking is a feature of Google Analytics that allows you to track actions whether or not a URL change is recorded. For Example: clicking on links, Form submit buttons, email addresses, social media icons, or video downloads. If you want to know How to track events in Google Analytics please visit this post.

5. Smart Goal:
Smart goal is not available in my account. I will explain it further once fully available.

In any case if you see the following form after clicking Goal button
add image goal form for a particular category selected

don't worry, you can select custom option and click next or you may also change category from property settings. You can select from no one to any relevant category to your industry. Please refer below image

Image Source: Google Analytics account

Remember: Once you created a goal you never delete it, you can modify it but can't delete.

Where you can see conversions in your Google Analytics account?

1. Just login to your Google analytics account 
2. Select the desired website profile if you have more than one website
3. Select the goals under conversion in left sidebar
4. Select overview under Goals