Searching for designs on the USPTO site is a bit tricky. I'll explain it step by step.
First, go to this link. This is the searchable design search code manual. Type in simple keywords that describe your logo. For instance, typing in telephone brings up the 6-digit codes for telephones, telephone poles, answering machines, etc. Make note of all the 6-digit codes relevant to your logo.
Second, go to this link. This is the main trademark hub page. From here you'll see 2 columns. Look at the right hand side for a link that's titled Search. Click on that.Now click on Structured Form Search (boolean). In the first search term box, type in the 6-digit code, no spaces & no dots. Change the field to Design Code. Stopping here will likely result in too many hits to look at so let's use the rest of the search boxes to narrow it a bit.
Change the operator to AND. In the next search term box, choose one keyword that describes your goods/services, e.g. clothing, software, etc. Change the field to Goods & Services. Now click Submit Query.
You should then see a listing of marks that you can view in more detail.
I've been in the trademark field for 14 years & I do not recommend that anyone conduct this logo search & consider themselves to be done. There are so many nuances within the USPTO as well as with trademarks in general that the likelihood of missing something is high. However, I feel the above provides a good snapshot of how involved searching logos can be & is a nice primer for those folks interested in protecting their logo.
You've got to keep the USPTO's guidelines in mind. Logos need not necessarily be exact to be considered a similarity. They take into consideration things such as similarities in Appearance or Meaning as well as similarity in industry. Your logo may look like one definite thing to you but you have to emotionally detach yourself from it & see all the inherent possibilities. It's those possibilities that will also have to be searched.