Here is one, of many, ways that you might organize this.

Since your example wants each result to depend on the value of the previous result NestList seems like a good choice.

Since you have three variables, c,d and t that you are interested in start with initial value of {0, 7, 0} to represent {c0,d0,t0}.

Write a function, call it f, that will be given {prevc,prevd,prevt} each time and it must calculate {newc,newd,newt} as a result.

f might start as f[{c_,d_,t_}]:=... Note those { } around c,d,t declare f is going to be given a vector of 3 elements as an argument

and it also must return a vector of the three new elements.

Note that you cannot change the value of c,d or t inside f, you can only calculate new values from these.

You might use Module to construct f so that you can have local variables and multiple statements separated by semicolons inside.

Then you use something like list=NestList[f, {0,7,0}, 100].

That should return a result like {{c0,d0,t0},{c1,d1,t1},{c2,d2,t2}...{c100,d100,t100}}.

Then c=list[[All,1]];d=list[[All,2]]; will extract your c list and d list and you can try ListPlot[ c] or even ListPlot[{c,d}].

Does this give you enough hints that you can see how to structure your solution?

Note that x/.FRoo only gives you the result of x when the value of FRoo is substituted. It does not then store this new value in x.

This is a somewhat common misunderstanding that new users sometimes fall into.

If you want to store a new value in x then you need to do something like x=x/.FRoo where there is both a replacement and assignment,

but remember as I wrote above, you cannot change the values of parameters of a function inside that function.

Note that it is possible to pack your entire problem inside the NestList without defining a separate function, and many do that,

but for new users I think it is less likely to result in confusion and errors if you write a separate function and concentrate all

your attention on getting that function right instead of trying to shove complicated funny notation inside the NestList itself.