Many countries have currently enforced entry bans or extra checks to curb the spread- same applies to parts of the European. Before you travel, check the situation in your travel destination carefully. To learn about the situation in EU countries, visit reopen.europa.de and check the website of RKI to find out which countries are currently considered as high-risk areas and areas where a virus variant is widespread. On auswaertiges-amt.de you can find contact information of the embassies and consulates in Germany.
For many countries, currently you need a negative test result or proof of full vaccination to enter. Within the EU, travelers can use the "EU Digital COVID Certificate" to prove vaccination. For some countries you also have to fill out an entry form. You need to inform yourself in advance about the entry regulations concerning your country of destination.
For many countries, the travel warnings issued by the Federal Foreign Office still stands. On the website of the Federal Foreign Office you can find all essential information. You can learn about your rights as a holidaymaker whose trip is affected due to the current situation on the website of the Consumer Center and the European Information Center Germany.