Welcome to the forum.
River Fishing by Len Arbury(?) is a good starter and low cost if you don't want 'book shelf' condition.
An free running centrepin is a must, as is a reel line that floats.
Use 5or6lb b.s. reel line and 2.5-3lb for your hook lengths, but scale up if there are barbel in your river.
Remember that river currents are linear, there is (usually) less current the deeper you go.
Go walkies downstream with your rod, net and minimal tackle and try every nearbank 'run' to get the hang of how to line comes off your reel and the float goes down, line,float and bait control is what your after.
Don't try and catch fish, just feed each run, strike at every drop of the float and learn what is a bite from a fish, minnow or weed, then fish the same swims on your way back upstream.
You will catch fish because every newbie does, why I don't know, but they do
Don't be afraid to ask anyone you meet for advice if they seem to know what they are doing.
Forget Wallis casting
mg: for the first few months or until you see someone actually using this cast, then sit and watch, then ask how.
Lastly, where are you based?