We conducted a year-long experiment among millions of new sellers on an e-commerce platform. The treatment group received access to a free and comprehensive online entrepreneur training program. With a 24% take-up rate, training raised seller revenue (1.7% ITT and 6.6% ATT) largely by inducing advertising upfront. This allowed sellers to purchase sampling and overcome the ``cold-start'' problem. To understand the net effect of training-induced ads, we develop a model of advertising under platform-guided consumer search and information friction; we also construct consideration-set data that matches the modeled environment. Overall, our results reveal the information friction on---and the signaling value of---advertising for entrepreneurs on increasingly congested digital platforms.