is the present tense indicative auxiliary, with both a 3rd person singular subject and object. digu
is the same tense, but with different persons. The subject and direct object are 3rd person singular, but the indirect object is 1st person plural. For an example, "eman du" would mean "she/he gave it" and "eman digu" would mean "she/he gave it to us". So in your sentence, you need to say "kontatuko digu" which means "she/he (hurrengo lagunak) will tell us..." In the case of transitive verbs you still need a direct object in Basque, even if it's not stated in the English equivalent, so really that sentence would be translated as "the following person will tell it to us a thing that happened today". These 3 part auxiliaries like "digu" are called NOR-NORK-NORI, whereas the 2 part ones like "du" are called NOR-NORK.
2. "zuri" means "to you". "dizut" means "I ... it to you." So, since the verb "esan" requires the person you're saying something to to be the indirect object.
Let me stop and apologize profusely for making a couple mistakes in my last post.
I was very tired.
Since you meant to say "I meant this" you would say "esan nahi dut". "esan nahi dizut" would mean "I want to say it to you" which isn't what you were going for. That was a mistake on my part.
Also, I overlooked an error in your last question. It should be "gaur gertatu den
gauza bat". I don't know the linguistic terms off the top of my head and I don't know any equivalents in languages you know, but the "-n" suffix means "that" as in "the dog that barked" and "-la" means "that" as in "I told you that the dog barked." I hope that made sense!