Building a portfolio before your first job
Without work experience in a new field, a portfolio becomes your main proof. Start with small projects you do on your own.
New graduates and people changing fields often get stuck in the same loop: openings ask for experience, and experience only comes after you are hired. A portfolio is one way out of it.
Pick a real problem
A project that solves a real problem says more than a course exercise thousands of people have done. Look around you: a family business still recording sales in a notebook, a community struggling with its schedules, public data nobody has summarised well.
Write up the process, not just the result
For each project, explain the problem, what you tried, what did not work and where you ended up. The process is the part recruiters read most, because it shows how you think.
Three projects explained well are worth more than ten with no story behind them.
Keep it in one place that is easy to open
Gather everything behind one link, and make sure it reads well on a phone. Put the link at the top of your CV, and have one project you can talk through in two minutes at an interview.
A portfolio does not have to be big. What matters is that each piece answers the same question as the openings you are after.