DIY retaining wall using treated lumber

[Kirk R.]

my old wood retraining wall is rotted out. 

Lowes has on sale for $2.50.

Severe Weather (Actual: 3-in x 4-in x 8-ft) Pressure Treated Landscape Timber

How would you attach these? nails? spikes? 

would the 3 inch or 4 inch of the new wood go against the old ties? 

How to meet match up the corners? 

I've got the space to justI'm planning leave the rotting ties & build around. 

Any hints or tips for success or how to do on the cheap? 

Also best way to cut tge lumber.  i have a saws all.  but it doesn't cut that straight (could be operator error! :)) 

thanks