I have been a recruiter for 20 years+. Here is what happens to a submitted resume:
1) If you are given a persons email to submit a resume it will go to that persons email. Now you have their email address and can follow up with your resume.
2) You send it to an HR inbox. This is where it gets tricky- in this case they are in most cases using a resume software key-word search to search your resume. It will tally how many times key words from their job show up in your resume. For example- if you are to applying to a customer service job that asks for past exp. and experience using Windows software, it will tally how many times "Customer service and Windows show up in your resume' and will rank your resume accordingly. This is why it's important to include all the key words from their job in your resume even if you only used windows a few times.
At the bottom of your resume you can type 'software experience' and type in ALL the software you have ever touched. Or 'mechanical experience' and list EVERYTHING. Don't worry if you have limited exp. with it- the goal is to get the interview where you can explain.
IMPORTANT- remember, in all medium size to large companies your resume is not being sent directly to the hiring manager! If they use screening software, HR will then screen the resumes the software ranked highest and not look at the others. And then they will forward the top 5 or whatever to the hiring manager who will tell them to screen these.
All of what I just typed may not be 100% true 100% of the time but from where I sit it's generally the rule.