Hi Garry,
Good luck with your career -Planning can be a very rewarding profession.
There are 2 main routes into planning. The first and probably the best is, as Mike suggests, to transfer into it after a reasonable amount of experience on site in construction projects. This gives you an excellent grounding in how things actually work on site, the required sequence and typical duration of construction activities, the types of problems which typically slow a project down, etc.
The second route is to go straight into planning with no experience, as a junior planner. Many people do this, master the software (typically primavera or asta rather than microsfot project), and never really learn much else. These are known as "keyboard jockeys" in the trade. You can earn a good living as a keyboard jockey, but without an understanding of how projects are constructed you will be limited to entering in information gleaned from others on the project team and running reports. -Not the most satisfying career in my view.
If however you are smart and committed, and are lucky enough to be working with more senior planners early on in your career (for this I advise trying to get your first job with a big company) you CAN learn enough to be a "proper" project planner without much previous site experience.
Site experience is probably the most beneficial thing to have up your sleeve as a planner, but it is not everything. It won't tell you how to read a P&ID, interpret a contract, prepare an extension of time claim, build a wbs, sequence design and procurement activities, write a management report, etc
Formal training in how to use planning software is in my view one of the least important things to have, since it's pretty easy to pick up the basics on your own to be honest. However a lot of planning jobs do specify experience with a particular planning software as a pre-requisite, so obviously a lot of hiring managers disagree with me on this.
NB: Of the most common software packages out there, training in Microsoft Project is the least valued by employers, since it is a typical Microsfot product in that it is very easy to pick up the basics, but somewhat limited in advanced functionality.