What will happen please ? First communion

keepingquiet

I would add as you are not Catholic (and I assume this is Roman and not Anglican, Catholic), then you are not allowed to receive communion but may be invited up for a blessing. No obligation again to do anything, but the priest may tell how to receive a blessing if you wish.

Usual method is to join the queue for communion but just cross your hands across your chest (hands on opposite shoulders to indicate blessing only

Things to note:
Parking - get there early or look for nearby car park. It will be rammed with relatives and friends
Seating - ask your inviters. My church had 65 children in 4 sessions this year. Each child had a row of 8 seats to allocate. If it is a free-for-all again get there early, or be prepared to stand.
Take a camera, but be prepared not to use it except before or later.

I attend a Catholic church here in Germany - because CofE isn't a thing, of course. The children go for their first Communion on the Sunday after Easter. The organisers realise that many attending won't be regular churchgoers and there is usually an order of service with clear instructions as to what to say, when to sit, kneel and stand. Some churches will just have a leaflet with the songs and the priest, chaplain, cantor or someone will announce when to do what.

My friend is a Presbyterian and nowadays there is much ecumenical cooperation - we all go to each others' churches. She was a member of the Catholic Women's group in her village for many years.