Kerning inside Photoshop
Kerning is the process of adjusting letter spacing in a proportional font. In a well-kerned font, the two-dimensional blank spaces between each pair of letters all have similar area. Wikipedia.
To add kerning between each letter in Photoshop you place the cursor between the letters and press Option+RightArrow on a Mac (or Alt+RightArrow in Windows). To remove kerning between each letter in Photoshop you place the cursor between the letters and press Option+LeftArrow on a Mac (or Alt+LeftArrow in Windows).
If you need an entire word or sentence kerned the same way, just select the group of letters and repeat the process above.