Familiarity with the basics might well help.
There’s a lot of different things involved in being a web developer. There’s the font end, stuff, server side stuff and some database stuff will be extremely useful to know.
HTML5, CSS3 and JavaScript would all be a good, start, then some jQuery and AngularJS. That’s some of the front end stuff.
Then for the server side you need to decide whether to go down the Microsoft route or the PHP route – these to my mind are the two main server side technologies.
If the Microsoft route appeals, C# is more prevalent than VB.Net so that’s the better one to concentrate on. It usually pays more, too.
SQL Server for the Mcrosoft route, MySQL for the rest.
This is a massive oversimplification of the subject and there are so many other areas to look into – doubtless others will be along to shoot me down.
The good news is that it’s pretty much all free to learn, the bad news is that you will very likely need a few years experience before you can freelance – unless you can persuade friends and contacts to let you sort their web presence out. Even then you would probably need to do a few freebies to get established.
It’s all doable – I used to work in sales of varying kinds before I made the transition to IT. In this country you would find a lot of people who say ‘But you are a civil engineer, what do you know about web development’ but your mileage may vary.
Just my thoughts – other views are available.
Good luck.