whats the experience to be a Communications system engineer ?

Hello. More information about that role can be found at this link:
https://apply.army.mod.uk/roles/royal-signals/comms-engineer-systems-engineer

Hi, as said above you can find out a lot of detail on the link. The qualifications required are: GCSE Grade A–C/9-4 in at least English Language, Maths and an IT or science based subject, for a quick reference.

In terms of other experience required there is nothing, other than the mandatory fitness. What I can say though is that CS Engineer is a technical role, so having an interest in technology / computing will be beneficial to you in training and beyond in the field army.

Once you have completed your training there are a whole host of different experiences / skills and qualifications you can achieve, some of which can also be seen on the link above. Feel free to ask if you have an interest in any particular area.