How should i prove every finite lattice is bounded? I want to know the outline to how to prove every finite lattice is bounded?
You can get a lower bound on two lattice points by taking their meet (resp. an upper bound by taking their join).  If a lattice has only finitely many points, this "two at a time" approach can be repeated (a finite number of times) to get a common lower bound (resp. common upper bound) on all the points.
Let the lattice $L$ has $n$ elements and the elements of the lattice is $a_1, a_2, \dotso ,a_n$

Now, $$a_1\lor a_2\lor\dotso\lor a_n= (\dotso((a_1\lor a_2)\lor a_3)\dotso a_n-1)\lor a_n)$$ [since $\lor$ is associative].

Since between $L$ is a lattice, between any pair of elements $a_i$ and $a_j$, $(a_i\lor a_j)$ exists,
So, $$(...((a_1\lor a_2)\lor a_3)\dotso a_n-1)\lor a_n)$$ does exist as well.

Similarly we can show if $L$ is a lattice with finite elements then a minimum element does exists.