Hi !
I've installed MikTex and then LyX.
I've seen in the tutorial that one can directly type the latex code. That is "click on the Tex symbol" and then there is a red box where I can type the formula.
However, in the tutorial, they're saying that if I type \gamma, it would produce the symbol and change color. But when I type it and then view it by DVI, I only get an error message, telling me to put the $ $.

Indeed it works if I put $\gamma$. But why ? Do I have to put $ $ every time I type a formula ?
Then, I tried to type
Code:
$\Gamma(s)=\int \limits_0^{\infty} e^{-t} t^{s-1} ~ dt$
And viewed it by PDFviewer.

The size is too small ! Especially the integral sign. How can I change it ?

Is it possible to modify a pdf that is already existing ?

And what is DVI ?

Is there a specific font you would advice me ?

They don't accept \mathbb{R}

how can I do ?
The questions may sound stupid, but I'm just a noob when it comes to get used to a new program
Thanks in advance !