This can be quite tricky, first define a system of equations:
ClearAll["Global`*"]
eq6a = x'[
t] == g * (y[t] Subscript[b, z][t] -
z[t] Subscript[b, y][t]) - Subscript[R, 2] x[t];
eq6b = y'[
t] == g * (z[t] Subscript[b, x][t] -
x[t] Subscript[b, z][t]) - Subscript[R, 2] y[t];
eq6c = z'[
t] == \[Gamma] * (x[t] Subscript[b, y][t] -
y[t] Subscript[b, x][t]) -
Subscript[R, 1] (z[t] - Subscript[M, 0]);
Use the solve command to solve it:
Solve[{eq6a, eq6b}, {x[t], y[t]}]
If that works use substitution to grab one of the variables, say :
s = First[x[t] /. Solve[{eq6a, eq6b}, {x [t], y [t]}]]
You'd think that you could just perform xfunc[t_] = s
but that WILL NOT work, instead you have to do a re-substitution in order for it to grab the value:
xfunc[blah_] := s /. t -> blah
xfunc[t]
The function name, as above xfunc[]
MUST NOT be x[t]
otherwise there will be some sort of recursive error and Mathematica will time out
So doing this all together:
Solve[{eq6a, eq6b}, {x [t], y [t]}];
s = First[x[t] /. Solve[{eq6a, eq6b}, {x [t], y [t]}]];
vfunc[blah_] := s /. t -> blah
vfunc[t]