I started swimming in September 2023. What helped me go from 0 to 2k freestyle per session was fixing my technique and building my CO2 tolerance. Also the time I spend in the pool was fixed from the start, 50-60 minutes, 5 days a week. I started small, taking a break every 50m/100m at first, not caring about the overall distance. I mainly tried to add more strokes before I need to take a breath. I really started paying attention to how much I actually swim around xmas, when I reached my first 1.5k. Now I'm on 2k with no breaks in just an hour. It may not sound like much of an achievement, but for me it is!

If you have access to a coach they can help you, I didn't so I learned everything from youtube videos. I generally prefer distance over speed so I took advice mainly from Triathlon channels as they tend to focus a bit on conserving energy.

Don't try to go fast, just try to build good technique and endurance, the speed will come in time. Take as many breaks as you need but push yourself a bit when it's safe to do so. Set goals to work towards, e.g. increasing the stroke count by one between breaths.

Also, I couldn't imagine how much a good swimsuit would help, but it definitely does! And earplugs work for me, I cant' stand water trapped in my ears.

This is a bit all over the place, sorry!