Prior to having a crack...I had (very) rudimentary programming experience (literally many years ago, and even then only beginner level). So I was kind of starting from scratch
If it's not clear to anyone...the world revolves around databases - your accounts software is a database, ebay's listings are a database, your website (if you have one) is a database. This very forum is a database...and so on.
Linnworks is essentially one very large database sliced up unto little bits that their paying customers use. So I realized I needed to learn about databases...now then, the industry standard is SQL, but an easier path is MS Access (as it has a lovely user friendly front end interface)...and literally that what I started on.
First learned how to construct a relational database...populating by importing data from excel/csv files (with for example customer order information exported from ebay, Amazon etc. Having got this working (& having learnt how to code using VBA), it quickly became tedious having to keep importing files...therefore I learnt how to code up an API (this is essentially a 'go fetch' instruction to your database - e.g. "go get all my ebay orders").
Not gonna lie, it's was one helluva learning curve...but it's like everything, baby steps first & then thinking "wouldn't it be useful/nice..." then working out how to do that.
There's nothing quite like the motivator of a deadline and as I said, Linnworks gave something like 4 months notification of their fees going from £0...to something like £1700. I'm so pleased they did, because that prompted me into action...and all the knowledge I've gained since, means I can pretty much self-deploy anything I need in my business (automation, labour saving tasks, forecasting/reporting etc.)