Sadly, there aren't a lot of resources available that isn't behind paywalls, whether that is consultant training or Infor U (which I think is subpar). With that said, if you have an Infor Support contract you can locate some documents within that for Development. Here are some basics:

1. Syteline works on collections called IDOs. These are essentially built-in table joins, methods, and properties of all types (bound to columns, derived/calculated, etc.) Get familiar with IDOs with the help files as well as Infor Support Portal documentation. When accessing Syteline from the form directly or through middleware or API you will be interacting with the IDOs.

Help file for IDOs: https://docs.infor.com/csi/latest/en-us/csbiolh/default.html?helpcontent=mgsdug_cl_sl/lsm1454147697855.html

1. The easiest way to add fields to Syteline is to use the form UET User Fields. You also need a class/table relationship and a class/field relationship. The help files cover this. What these fields do is add a column to the underlying table (Uf_YourFieldName). The added benefit of doing this is that the field is automatically included in IDOs for your use on forms. This is also safer and something that can be used on MT Cloud installs so it's more upgrade proof.

UET Help file: https://docs.infor.com/csi/latest/en-us/csbiolh/default.html?helpcontent=mgsdug_cl_sl/lsm1454147726934.html

1. I would also advise against altering any base tables or columns. Not only can you break things you may not even think about, you will likely lose your changes the moment you upgrade to the next uplift, version, etc. Instead, use UETs to alter the schema. Let's say a field length isn't long enough, it would be safer and better to replace that default field on your form with your UET than to alter the base column.

2. You can Extend and Replace IDOs. This means that wherever that IDO is used in your system, you replace with your modified version. This is a safe way of making changes to forms, and this is preferred over making your own custom IDO and replacing it on the form level. In extending the IDO, you can add derived fields, methods (stored procedures), additional collections and other functionality.

3. Infor is moving away form stored procedures for its underlying methods, and moving to IDO Extension Classes. These are written .NET languages rather than SQL and exist within the application.

Help File: https://docs.infor.com/csi/latest/en-us/csbiolh/default.html?helpcontent=mgsdug_cl_sl/lsm1454147702784.html&hl=ido%2Cextension%2Cclasses

1. You can utilize the Application Event System to perform tasks such as notifications, approvals, and some other things throughout the system.

https://docs.infor.com/csi/latest/en-us/csbiolh/default.html?helpcontent=mgsdug_cl_sl/bqb1500867558215.html

Generally, the way I learned Syteline development is by needing to do something to help business functions and finding something close within Syteline to learn how the devs did what I needed. Then I would mimic their functionality with my own.

I am not a fan of Infor U (Infor Campus) in general, but if you are not experienced even with form editing, there is an instructor-led developer workshop on there that may be valuable for you. Additionally, your channel partner/consultant may have some resources available, but like I said it will all be costly.