If you are in Berlin without a visa, or are on a Schengen visa, you are not allowed to work. To be allowed to work in Germany and Berlin as a refugee, you need an appropriate residence permit (Aufenthaltserlaubnis). You can apply for this online in Berlin. Go to the online application. Please note that you first need to register.
The basic work permit is issued together with your residence permit and noted on this, even if you do not have a specific job offer yet. When you submit your online application for your residence permit, you will receive a PDF document as confirmation. This certificate immediately allows you to work. The residence permit for temporary protection in Germany is issued for an initial period of two years. It allows you to access the guidance and referral services provided by the employment agencies (Agenturen für Arbeit).
Further information and practical offers of assistance and referral are available on the Information page for refugees from Ukraine of the Federal Employment Agency.