Process to marry mexican citizen?

Don't marry her while she's on a tourist visa. Apply for the "fiancee" type visa that'll allow her to remain in the US after the wedding. 

Well first off you can get a fiance visa probably that lasts longer than a tourist visa.  But she would apply for a green card after you are married.

If you need help there are immigration lawyers.

The actual marriage is pretty simple, and no different than marrying anyone else.

The immigration process is more complex. Here is the website:

https://www.uscis.gov/green-card/green-card-proces...

You can do it yourself if you're reasonably smart and good at following directions. Otherwise you can engage an immigration attorney to do it for you.

state.gov website -- see spousal visa/green card.  or your local immigration attorney

The actual marriage is very simple.  The two of you obtain a marriage license wherever you want to have the ceremony and then have the ceremony performed. Voila!  You are married.

However, you sponsoring her for immigration is much more complicated.  USCIS is very suspicious of someone who enters the USA as a tourist, marries a US citizen, and applies to adjust status so they can stay.  USCIS generally decides the non-citizen lied when they entered the USA by failing to say they planned to marry a US citizen during the visit. Lying about the purpose of the visit is a felony and will result in her application to adjust status being denied and probably her being banned from the USA.

Better would be for the two of you to marry and then she returns to Mexico ON SCHEDULE while you sponsor her for a spouse visa.  She can continue using her B2 visa to visit you, BUT she will need to convince the Immigration Officer she is only visiting and isn't trying to circumvent the immigration rules.  

Warning:  DON'T "just get married" assuming everything will be OK. It won't. 

If your own government can't provide you with the answer to your question why would you expect us to know?