Depends on where you start. Are you a pupil or student? Start by creating your own homepage, create websites you think are cool, and once you think you got it take a look at small local businesses. They usually don't have websites or old ones, and you can offer them to create a website for cheap money. While you get some pocket money (a few hundred € or $ a month), they get a site for cheap. When you look for a job, you can use all those websites as reference for professional work experience on your CV, plus you already had to deal with customers, which is invaluable. Customers and stakeholders usually are difficult people to deal with, and the earlier you learn how to handle them, the better.
However, if you already have a job and want to change to front-end, it's a bit different. Especially if you have no experience or knowledge at all, you will have to spend quite some after-hours learning. Depending on where you work, you might want to try to talk to your boss or HR department. They will be able to move your headcount to a front-end position without going through an application process. Alternatively, they might try to find a project, which you can use to learn side-by-side with a senior developer who shows you the ropes.
If you have to apply at another company to get a front-end position, you should try to build a portfolio. I recommend getting involved with opensource projects. They usually have open user stories of varying difficulty, which you can use to learn and improve yourself while getting feedback from other devs and professionals. Also, you can write your involvement onto your CV, and it will count as the experience you need to score a job.