The drawing of genetic crosses
The cross you're studying is Mendel's monohybrid cross. Which looks something like this.



Now here, the genotype of F1 gen plants is Tt. 

To draw this cross, proceed exactly like you decided. Draw the 2/2 grid and cross the alleles Tt x Tt

Your cross should look like this (ignore the plant drawings):



(Source: classes.midlandstech.com)